Exorcist Head

In most forms of media, a character is shown to have the ability to dislocate his bones in very bizarre places. The most popular way is turning your head 360 degrees before facing the front again. Can fall into either Squick or Nightmare Fuel for some people.

Often done as a Shout-Out to the Trope Namer, The Exorcist.

Subtrope of Abnormal Limb Rotation Range, Compare Body Horror, Losing Your Head.

Examples of Exorcist Head include:

Anime and Manga

A rather gross and unsettling example of this trope shows up in Boogiepop Phantom.
It happened in the first episode of Sailor Moon. But it only appeared in the Japanese version.

Comic Books

The Owl, a Daredevil villain, can rotate his neck 360 degrees like his namesake.

Fanfic

Jack's evil form from Calvin and Hobbes: The Series does this just a bit after fully face heel turning.

Film

The Trope Namer is the 1973 Horror film The Exorcist.
Played for Laughs in Little Nicky when Nicky (son of Satan) performs this again to his buddies.
In Beetlejuice, apparently this happens to the titular ghost at random.
Done as a parody to The Exorcist by the magical cartoon physics baby in Son of the Mask, when his worn-out and nearly out of his mind father suggests he take him to a doctor, and then an exorcist.
Death Becomes Her, one of a pair of Alpha Bitches, Mandy, (now made immortal by a magic potion) falls down the stairs and cracks her neck. Not only does she survive (or un-survive) the fall, she gets back up with her head twisted completely backwards, facing her backside. Although her head is reoriented to its proper position, it leaves her with a bone protrusion on her neck.
Pops up naturally in the Exorcist parody Repossessed.

Film, Animated

Pinocchio does this in Disney's 1940 film.
Woody does this in the first Toy Story film as a Shout-Out to The Exorcist.

Live Action TV

In the Small Wonder episode "My Robot Family", Vicki does this in response to the command "about face".
In The X-Files episode "The Amazing Maleeni", the eponymous magician does this as part of his act. Mulder and Scully never do figure out how he did it.
One early Buffy the Vampire Slayer episode has a giant praying mantis in human form. Early tip-off: She "does a full-on Exorcist twist" when she hears someone come up behind her.

Video Games

Mimi in Super Paper Mario does this upon revealing his true form in the game's second chapter. However, instead of twisting her head around, she somehow spins her head on her neck, causing her head to turn upside down.
Havik from Mortal Kombat has the ability to contort his entire body in odd and sickening ways. In fact, two of his specials allow him to regain health by doing so.

Western Animation

The Flying Dutchman actually did this twice in SpongeBob SquarePants.
One Treehouse of Horror episode has Homer Simpson doing this, parodied in some way.
- In The Simpsons episode where Homer and Marge are declared unfit parents and the kids given to the Flanders family to foster, Ned takes them to the river to baptize them. Bart and Lisa are sitting in the back seat and Maggie is in front.

Maude: Oh, relax, Bart. Your sister Maggie isn't scared.
Bart: That's because she can't talk.
Maggie: [pulls her pacifier out] Daddily doodily!
[she turns her head 180 degrees to face Bart and Lisa]

- Maggie also does this in the very first Treehouse of Horror, in a nod to The Exorcist.
Done by a Creepy Doll on Jimmy Two-Shoes.
Done by Omi, of all people, in Xiaolin Showdown after he makes a temporary Face Heel Turn and joins Chase Young on the Heylin side when he gets his good chi being left behind in the Yin-Yang world, coming back with only his bad chi remaining. When the remaining Xiaolin apprentices try to restrain him so they can restore his chi, including trying to sneak up behind him during his rampages, Omi makes a complete 180 degree head turn, complete with Ax Crazy grin, Red Eyes, Take Warning, and the sound of scraping metal.

Real Life

Owls are famous for being able to turn their heads extremely far in either direction. Unlike many animals like humans, owls lack the special muscles in their eyes that would allow them to rotate or roll, leaving them fixed.
Praying mantids are the only insects that can look over their shoulder. A praying mantis can turn its head more than 180 degrees and can see movement up to 60 feet
There are people recorded to be capable of turning their heads 180 degrees, like this example http://www.youtube.com/watch?v=bHjRORiMl7E