Twin Telepathy

Kim: Ron, why can't my brothers be normal?
Ron: They're relatively normal. For twins, I mean. At least they don't speak their own weirdo language.
Jim: Hikka-bikka-boo?
Tim: Hoo-shaw!

—Kim Possible, "The Twin Factor"

In fiction, at least, it is common for twins - especially identical twins (or brother-sister twins who seem otherwise identical) - to seem to share a Psychic Link, even in series which do not otherwise have any paranormal element. This connection may vary from a vague feeling of when the other twin is in danger, to continuous telepathic communication, to being an outright Hive Mind. They often experience each other's injuries as part of their link, and frequently finish each other's sentences. In a very few cases, the siblings involved are not twins.

Thanks to the Mindlink Mates trope, this level of closeness can lead to other interpretations of their relationship.

Compare with other types of Psychic Links.

Related to, but distinct from, Single-Minded Twins.

Examples of Twin Telepathy include:

Advertising

This Pepsi commercial hilariously uses this trope with twins Separated at Birth (both played by Rick Moranis).

Anime and Manga

Toyed with in the case of Shagia and Olba Frost from After War Gundam X, since they have this power yet it's not fully explained if they're normal siblings or fraternal twins.
The Comic Book Adaptation of Breath of Fire IV plays up the Twin Telepathy betwen Ryu and Fou-lu far more than the original video game (which merely hinted at Twin Telepathy for the most part). In fact, the connection between the two which is entirely justified as the two were Split At A Failed Summoning is an integral and vital part of the manga's plot.
In A Certain Scientific Railgun the Sisters network is somewhere between this and a Hive Mind. Granted, they're mass-produced clones who were specifically engineered to share their thoughts this way.
Used in the Fatal Fury movie between Half-Identical Twins Laocorn and Sulia. At first it's simply an empathic and telepathic connection, but after Laocorn becomes an invincible Physical God, the connection was ratcheted up to the point where Sulia's self-inflicted wounds weakened her brother, and her suicide effectively both shut off his invincibility and released him from the More Than Mind Control state he was subjected to..
In Fushigi Yuugi, Suboshi learns of his twin brother Amiboshi's "death" because he can no longer sense his presence.
Trigun Maximum has a pretty literal example, with Knives's ability to invade Vash's mind and the plants' general ability to communicate with each other over great distances. When Knives is using his power, Vash can also 'feel' it from kilometers away. On the other hand, they disagree on almost everything and really don't understand each other. In fact, they suffer from a really bad communication breakdown.
In the manga of Ouran High School Host Club, during the test of courage chapter. Hikaru and Kaoru are separated, and the latter gets locked in a classroom. Hikaru somehow manages to find Kaoru and explains that he had heard his twin's voice telling him where he was, even though Kaoru had no way of telling his twin his whereabouts and Hikaru could not have found out through someone else.
Ako and Riko from Kiss×Sis tend to know when the other is up to shenanigans. They even Lampshade it when one of them is having a particularly Ecchi Imagine Spot by the other one calling them out on it.
Seen in Volume 8 of Arisa; as Tsubasa is hurt, Arisa flatlines in the hospital, and Tsubasa even says not to underestimate the bond between twins as she races to help Arisa.
Sorta used in the Vampire Princess Miyu manga, with the Minami twins. Eldest twin Rima can't leave their home because she's a fullblooded mermaid who lives in a tank, but she can see the outside world through the senses and specially the eyes of Mari, the youngest twin.
Miracle Girls is based on this trope; the main characters are identical twins with psychic powers, including telepathy with each other. (Although there have been instances where they were able to communicate with other psychics.)

Comic Books

X-Men did this with the Stepford Cuckoos, creepy psychic quintuplets (though two have since died). They are clones of non-twin telepath Emma Frost. Also, there were a thousand of them at one point. They are separate entities, but sometimes the same sentence will run between two, three, or even five connected speech bubbles.
- This creates an interesting situation in terms of punishment. Its revealed during a mini-series that Emma "grounds" the Cuckoos by telepathically locking them in their own minds so that they can't communicate with each other like they normally would
In Elf Quest, the maximum "sending range" (range of telepathic powers) is important to the plot on numerous occasions. Sending across the Vastdeep (ocean) requires a powerful magic amplifier. But twins Suntop and Ember, despite actually having distinct genetic code (one immortal, one wolf-blooded), can contact each other from halfway across the world, and know when the other is in distress.
- Then again, a weaker version of this connection is used for the entire family, and for any close kinship relationships the series over: They feel hurt and loss even without direct sending. The Wavedancers are particularly attuned to the loss of their tribemates.
DC Comics Kobra series had twins with a physical telepathy (they felt the other's pain). Just after the end of the series the evil twin found a way to kill the good twin without dying himself.
It depends on the writer, but Jade and Obsidian had a sort of vague empathy/danger sense regarding the other about half the time.

Fan Works

Double-subverted in Drunkard's Walk VIII: Harry Potter and the Man From Otherearth. In it, the Weasley twins admit to Doug that any Finishing Each Other's Sentences they do and any other evidence of Twin Telepathy they demonstrate are all an elaborate gag, based on one twin coming up with a reasonable, contextually-appropriate response to the other and counting on the fact that no one else would know what was going to be said or done, anyway. Later, though, Doug witnesses what he believes is evidence that they really do have Twin Telepathy, and that the mundane explanation they give for it is the actual gag.
Discussed -- or at least thought about -- by Hermione Granger in the Harry Potter fic The Arithmancer after witnessing several instances between Fred and George.

Film

In The Boondock Saints, the twins receive their calling from God at the same time. As they were both asleep before it happened, it's debatable whether it was Twin Telepathy or actual divine interference. The sequel plays with the ambiguity some more by having the twins act antsy about their past as The Saints before the plot kicks off.
The Octopus in The City of Lost Children is practically a Hive Mind, and is referred to in the singular.
In Hellboy II: The Golden Army, Prince Nuada and Princess Nuala can read each others' minds. It's also an instance of Synchronization, as an injury to one is an injury to the other.
A partial example in Nadja, where Edgar is sometimes able to feel what Nadja is thinking and feeling.
In Star Wars, Luke and Leia have a connection despite having been Separated at Birth, which conveniently doesn't appear until a crucial moment in the second film. (This may have more do with the fact that both of them are strong in The Force than with them being twins, though, as Luke demonstrates a similar connection with his father.)
- Similarly, Jacen and Jaina (Han and Leia's twins in the Expanded Universe) have a "twin bond" which goes much deeper than the usual connections between Force-users, as do Luke and Leia.
  - Notably, the telepathic bond second to their own is with their younger brother.
In Tom and Thomas, the titular children share a psychic link with one another, even though they were separated soon after birth. Tom & Thomas "talk" to one another and even feel each other's pain at times. At one point, Thomas gets tripped in class, and at the same time Tom falls down.
Happened as a source of comedy to the twins played by Jackie Chan in Twin Dragons.
Experienced by Julius and Vincent Benedict (Arnold Schwarzenegger and Danny DeVito) in the 1988 film Twins, complete with Synchronization, much to the latter's discomfort.
The Corsican Brothers by Cheech and Chong, very roughly based on the Dumas book of the same name. The film plays the central concept for slapstick, with the brothers hitting themselves to cause injury to the other.

Literature

Older Than Radio: Twin Telepathy is one of the main plot points of Dumas' The Corsican Brothers.
The novel American Gods had a very minor side story about a set of twins with a form of Twin Telepathy. When one of them lost his arm, his sister's arm shriveled up and became useless, even though they were geographically separated and there was no way she could even have known about it.
From David Eddings' The Belgariad/Mallorean series come the twins Belkira and Beltira. Not only can they communicate with each other, but functionally have a single mind, such that they are used to read two separate prophecies to find similarities between them. Only one character can reliably tell them apart, since they do tend to finish each other's sentences.
- From the same series, Polgara and her twin sister Beldaran. This is explored in much more depth in the actual Polgara book, as Beldaran had a normal lifespan compared to Polgara's The Ageless-style immortality, and is thus long since dead.
In P.C. Hodgell's Chronicles of the Kencyrath, protagonist Jame and her fraternal twin brother Torisen have moments of intense connection, sometimes in dreams and sometimes in waking life. He, though, is in denial about this and many other strange things that happen around him.
The main characters of both Song of the Lioness and Daughter of the Lioness by Tamora Pierce are twins; each shares an empathic link with their (male) twin, but neither can read their brother's mind.
- In Cold Fire, the third book of the The Circle Opens series, also by Tamora Pierce, the main character teaches magic to a pair of twin girls who have this kind of connection, although, as in the previous example, it is more empathic than telepathic, and appears to be mostly restricted to knowing when the other one is hurt or in danger.
Dexter comments on the apparent telepathy between Astor and Cody (sister and brother, she's three years older). Judging by his comments in the novels, either he's noticing it more (and finding it more worth mentioning) or it's getting stronger as they get older.
- Dexter himself seems to experience this, at least in the novel, with his older, almost identical, brother, Brian, to the extent that Dexter often finds himself inadvertently observing Brian's murders and on at least one occasion instinctively knowing his location, initially leading both he and the reader to suspect that Dexter may be the real Ice Truck Killer.
In Dead Beat of The Dresden Files, Harry notices a pair of twins in the pub that he knows by sight that have twin telepathy. In the scene, they're playing chess together, which (amusingly) Harry finds somewhat masturbatory.
In the first book of the Evil Genius Trilogy, Jemima and Niobe (AKA Jem and Ni) are psychic twins that used their telepathic link to coordinate several successful burglaries, until they were enrolled in the Axis Institute. Unfortunately, their bond doesn't survive the strain of the coursework, and their part in the novel ends with Ni stoving Jem's head in with a computer monitor.
The Weasley twins in Harry Potter, especially in the movies. It's implied that they do this just to mess with people's heads. This tends to get exaggerated in fan works (the telepathy, not the messing with people's heads, although that gets exaggerated, too).
In Mercedes Lackey's The Last Herald-Mage trilogy, one character has this with his twin. Then one of them dies, showing the reader that twin telepathy can be a bad thing.
The twins in Spider Robinson's Lady Slings the Booze have this to such a degree that they're basically one mind in two bodies.
Samneric (Sam and Eric) in Lord of the Flies. Identical, inseparable, and finish each other's sentences.
In The Midnight Twins by Jacquelyn Mitchard, this is pretty much the whole point of the book. Twins Meredith and Mallory Brynn, despite being complete opposites, can communicate with each other telepathically(which they sometimes use for cheating on tests) and even have their own elaborate made up language, complete with past and future tenses.
The Power of Five's Jaime and Scott Tyler's power; both can read minds but decided to read each other's minds instead of other people's because of the evil thoughts humanity can possess.
In Julian May's Saga of the Exiles tetralogy, twins Kuhal Earthshaker and Fian Skybreaker are so closely linked that they more-or-less form only one person between them.
The twin brothers Jacob and Alex Teller of The Shapeshifter series have psychic link as well as a knack for impersonations.
In Slapstick, by Kurt Vonnegut, the main character and his sister can think as one and combine their intelligences if close together.
Kathryn Lasky's Starbuck Family series of juvenile mysteries features two sets of telepathic twins: Half-Identical Twins Liberty and July, and their identical younger sisters, Charly and Molly. Their Twin Telepathy allows all four to communicate with any of the other three, despite the pairs being several years apart in age.
In The Stone Prince by Fiona Patton, a novel about a royal family touched by the gods, two of the characters, identical twin princes, are linked Seers. They were Siamese twins at one point (broken apart during birth) and have complementary powers—one gets his visions at night, the other in the daytime. As knights, they fight cooperatively, without thinking, and other sets of twins in the realm try to imitate their style. And finally, when one goes insane, the other nearly goes with him. Since inheriting the throne would involve literally becoming the vessel of their God, that too would be problematic Would the God know which one of them was first-born, or would It take both of them? If it picked on one, what would happen to the other? There are hints that this has indeed happened in the backstory, and that it ended badly. Oh, and they sleep together, though no sex is implied.
The Angevin Empire of the Lord Darcy series does the same in Michael Kurland's A Study In Sorcery, using Twin Telepathy to send covert messages across the Atlantic and keep real-time tabs on their New World settlements. Only thirty-six people are entrusted with the secret of this communication method.
The Robert A. Heinlein juvenile Time for the Stars uses Twin Telepathy to achieve superluminal communication.
In Heinlein's Time Enough for Love, Opposite Gender Clone twins Lapis Lazuli Long and Lorelei Lee Long claim to possess this. It's never verified (and the other characters display an uncharacteristic lack of interest in exploring the phenomenon), but they do talk in Finishing Each Other's Sentences and generally behave like Single-Minded Twins.
Elizabeth and Jessica Wakefield are shown to have instances of Twin Telepathy in the Sweet Valley High series, although it only seems to manifest at plot-relevant moments.
Bran and Matthew Maddox of A Swiftly Tilting Planet possess the ability to sense what the other is feeling.
In Warrior Cats, Squirrelflight and Leafpool had this in their earlier books.
Kestrel and Bowman Hath, the main characters of William Nicholson's The Wind on Fire trilogy, have this for no adequately explained reason. Actual telepathy, not just an empathic connection.
Two randomly-introduced young characters in the otherwise entertaining Young Wizards series' eighth book walk up to Nita on the Moon and subsequently: finish each other's sentences; declare in stereo that they're a "Twychild" (apparently, that's Speech for "annoying twins with a hive mind"); burst into laughter as if talking in sync with each other is some sort of awesomely hilarious novelty that everyone should be amazed and delighted at; and then walk away. How the main characters did not find this irritating is a mystery to many.
They aren't exactly twins, but in The 39 Clues, Amy and Dan can sometimes tell what the other is thinking just by looking at each other.
In The Bad Place by Dean Koontz, the characters Verbina and Violet have this as well as the ability to form a telepathic link with all nonhuman animals.
This is pretty much a given at Sevenwaters, both between twins (there's a set in every generation) and between Sorcha and several of her brothers.

Live-Action TV

Played with in one episode of Cheers. A character who's pregnant with twins stops a pair of adult identical twins as they're leaving the bar, and asks if it's true that twins can read each other's minds. They stand there silently for a second, and she says, "Well?" One responds, "Oh, we're discussing it."
The Babylon 5 verse already has non-twin telepaths. The Centauri, however, place special value on telepathic twins, using them as the Emperor's personal communication system despite the presence of the much more mundane FTL radio in that verse. The Centauri Court upholds old customs and imperial decrees almost religiously, so that may be why they still use the twins.
In Star Trek: The Next Generation, a species called the Binar are all born as twins with built-in telepathy.
In Deep Space Nine, the Miradorn are all like this, and if one twin dies, the other suffers in ways that weren't made perfectly clear (but the remaining twin went on a crusade to kill the one who killed his twin, and considered this "all he had left.")
- The Miradorn and their Twin Telepathy are explored in detail as part of The Cleanup, a novella from the Starfleet Corps of Engineers series.
In Star Trek: Voyager, a pair of twin boys rescued from the Borg quite possibly shared this trait,^{[please verify]} if only because they were Borg.
The Creepy Twins in The X-Files episode "Eve". Though raised by different foster parents 3000 miles apart, they "just knew" about each other's existence and murdered their fathers in the same unusual manner.
Gem and Gemma from Power Rangers RPM take this to its logical, creepy conclusion. They show every sign of being incapable of independent thought, speech, or action for their first several episodes, though they got better when Gemma started seeing a guy (namely, Flynn.) Gem wanted no part in that, so they developed on-again off-again individuality and the ability to speak independently on occasion. Each got A Day in the Limelight apiece of being featured as an individual.

Gem: We don't
Gemma: split up
Gem: Ever!

The Suite Life of Zack and Cody: Zack says he'll use his twin telepathy to get Cody, explaining that twin telepathy is how he knew Cody broke his arm that one time. Carrie says Zack is the one who broke his arm.
- Also used in "The Suite Smell of Excess" as Carey's excuse for them dreaming about the same alternate universe. Or Was It a Dream??.
This was the central premise of the British kids' show The Gemini Factor. Two teens, a teacher's pet girl and a rebellious boy, meet and start having Psychic Link flashes. Turns out, of course, that they're twins who were Separated at Birth.
In Jekyll, the protagonist's twin sons display some form of this in the end, when they imply that they are able to "switch bodies." However, they are fraternal twins rather than identical.
Tracker had a race called Orsians who were always born in pairs and each set of twins had a telepathic link to one another.
The episode of The Wizard "Gypsies, Tramps & Thieves" has a girl starting to have psychic visions of her twin, fostered by evil gypsies.

Video Games

A core part of the plot in the Mega Man Battle Network games, where it functions between the material world and the Internet. In over half the games, part of the gameplay, too.
In Final Fantasy Crystal Chronicles: Ring of Fates, Yuri and Chelinka can speak telepathically with each other after the Time Skip, since Chelinka lost her voice after watching their adoptive father die. She's slowly trying to get better, though.
Slight subversion from the Code Geass Nintendo DS game: though the main villains are psychopathic twin princes Castor and Pollux, only the former possesses Twin Telepathy; Pollux has a superior version of Lelouch's own Evil Eye.
In Pokémon Ruby, Sapphire, and Emerald; the Mossdeep Gym Leaders are fraternal twins that finish off each others' sentences (appropriately, their specialty is the Psychic type). You then have to fight in a double battle instead of the normal single battle. In the anime, Tate and Liza didn't display many traits of this.
Second Sight, two minor characters featured were Tanya and Ivan: according to Dr Grienko's notes, these twins are both psychic, and as such possess not only the standard Psychic Link but also telekinesis and other powers. However, these powers are only active while the two are in close proximity; once they're separated, the twins are powerless.
BloodRayne featured a pair of psychic Nazi twins who were born as conjoined twins and then separated. Attacking one hurts the other. They're probably among the most sympathetic villains in the game.
In Yoshi's Island, the Yoshi only know where to find Baby Luigi because of Baby Mario's link with him.
There are several bosses in World of Warcraft that hinge around a twin theme. They tend to have identical (or complementary) abilities and share a single health pool. Oftentimes the encounter is staged such that you have to kill both of them within a short time window (say, fifteen seconds) or the dead one will resurrect and you'll have to start over. Another common mechanic is that when one twin dies, the other inherits their twin's magical abilities.
- Lady Sacrolash and Grand Warlock Alythess are collectively known as "The Twins" encounter in The Sunwell.
- Eydis Darkbane and Fjola Lightbane are a Yin Yang themed pair of twin Val'kyr in the Crusader's Coliseum.
- Morchok and Kochrom (see what they did there?) are completely identical—they even have the same move set. Kochrom appears only in the heroic version of Dragon Soul.
In Final Fantasy IV: The After Years, Porom knows when Palom's in trouble half the world away. This might seem odd, given that the two are Polar Opposite Twins, except for the one thing both have in common: magical prowess.
A subversion of sorts: They're not related at all, but this trope was the prime reason that many players assumed that Link and Zelda were twins (or at least siblings) in The Legend of Zelda: A Link to The Past. The characters share a telepathic bond through much of the game, and Link's uncle's final words in the English version were to tell Link that "Zelda is your...", which many people thought was supposed to have been finished by the word sister. This line was removed in the Game Boy Advance port, and re-added (although slightly different in the American translation) in the Bonus Dungeon when you encounter a boss pretending to be your Uncle.
You can debate whether you want to call them twins, but Luke and Asch have a mental connection that allows them to speak to each other. It's one-sided, though, as Asch is the only one that can initiate it between himself and Luke. Lorelei can speak with both of them, but again it's one-sided.
- This could possibly be attributed to quantum entanglement, as the clones are supposedly replicas using special vibrating particles of magic that match the original

Web Comics

Subverted in CRFH!!!: when Roger's Half Identical Twin sister Lily tries to read Roger's mind, she manages to almost correctly divine the major events of the past four months in-story, except reversing or twisting around the details (e.g., she claimed he'd shot God with a Satanic missile, when in fact he's shot Satan with a blessed shotgun). Roger dismisses this as coincidence, a strange attitude for someone who was so immersed in the bizarre.
Mary and Sue have this in Dubious Company. Sal refers to it as the "upgraded" version of twin empathy. It is not without its downside. When Mary becomes The Mole, she gushes over Elator more often than providing useful information. Cue Sue smashing her head into the table to turn it off.

Western Animation

The twin bounty hunters I and Am in Samurai Jack.
In the Western cartoon Silverhawks, Steel Heart and Steel Will had such a link.
Yin and Yang from Yin Yang Yo exhibit rare flashes of this when they're separated and in trouble.
In Kim Possible, the heroine's younger twin brothers often display examples of this trope.
Li and Lo in Avatar: The Last Airbender have synchronicity, so they may possess this.
In the 80's G.I. Joe cartoon, identical evil twins Xamot and Tomax displayed this and synchronicity as well.
Mas and Menos of Teen Titans apparently have this, as Mas was able to sense when Menos was frozen.
He-Man and the Masters of the Universe and She-Ra exhibited instances of this trope from time to time, although not frequently.
Invoked on Young Justice, when Superboy and Miss Martian go undercover as supervillain twins. Since Miss Martian is psychic, Superboy explains their connection as being a result of this trope.

Real Life

According to various real-life stories, this trope is indeed Truth in Television, at least occasionally.
- In an episode of Iron Chef America, guest judges Tia and Tamera Mowry noted that the challengers, identical twin chefs Nicola and Fabrizio Carro, were a lot quieter than everyone else and communicated more with slight glances and motions. The girls said they did the same thing. Of course, that comes more from simply being extremely familiar with each other than anything that would mean kicking one means the other feels it.
- A pair of French identical twins, appropriately known as "Les Twins", are a dance duo that have said that they can "feel what the other is going to do before he does it". This can be seen in their freestlye dance battles, where the two are effortlessly in sync with one another.
Horrifyingly tested by the Nazis in World War II. Mengele in particular was fascinated with identical twins and would perform experiments to see if they could feel each other's pain or distress by separating them and giving one good conditions and then torturing or inducing diseases in the other.
A somewhat less fantastical possible explanation for identical twins, at least as children while their environment has been mostly the same, seeming to know each other's thoughts and mimic one another's actions unprovoked: given the same genetic predispositions and similar parenting and resources, they're wired to have predictably similar thoughts and actions, and to make similar decisions given the same stimuli. Which means the real life examples are rather Single-Minded Twins; just not as extreme as in fiction, of course.