The Ketchup Test

This is the infuriatingly illogical scene found in many action films, in which a character touches a blood stain with his fingers, seemingly in order to make sure that it's blood. In Real Life, doing this is a good way to get yourself implicated when the lab analyzes it, or at least brought up on charges of tampering with evidence. Oh, and did we mention you've just found a lovely new home for any viruses or bacteria the victim happened to be carrying?

Sometimes it turns out to be ketchup or strawberry jam, especially if another character has been doing a Chicken Little impersonation over the supposed bloodstain. In Real Life, it's possible that some animals (bloodhounds, brown bears, tyrannosaurs, larger sharks) may have a sufficiently powerful sense of smell, this (or simply sniffing the blood) might actually allow them to determine the species or even the individual victim involved.

See also Sniff Sniff Nom, Fingertip Drug Analysis. Not to be confused with The Ketchup Advisory Board.

Anime and Manga

 * Inuyasha claims he can do this. Of course, he's a dog hanyou.

Comic Books

 * In a Marvel Comics Dracula story set during World War II, Dracula identifies a bloodstain as "gypsy blood" this way. Well, he is a vampire... (Nazi troops were killing Roma. The Roma in Transylvania are protected by Dracula. Bad Move.)
 * Lehrigen, a human from the Wild Hunt subseries of Elf Quest, is an expert hunter and tracker, and can tell human and elfin blood apart by smell and/or taste.

Fanfiction
""Walking dead and raspberry jam?" Maude complained. "There's raspberry jam on the votive candles! What kind of chapel is smeared with raspberry jam?"
 * In The Keening Blade (Dragon Age) the slightly-mad Maude samples the bloodstains available in Warden's Keep:

"What kind of chapel is full of mindless zombies?" Loghain wondered, laying another one low.

"All chapels," Morrigan shot back. "And that looks like blood to me. How do you know it's raspberry jam?"

"I tasted it," the girl replied loftily, finishing off the last of the monsters. "It's not blood, it's raspberry jam. I checked."

Kicking a skeleton aside, Loghain snarled at her. "Didn't your parents ever teach you not to put strange red substances in your mouth?" He thought again. "Or any strange substances?"

"I know about mushrooms," she replied. "I'm not an idiot, you know.""

Film
"Col. Worf:"
 * Dumbledore in Half Blood Prince. "Dragon blood."
 * Gimli tops it by tasting the orc blood in Peter Jackson's rendition of The Lord of the Rings...which raises the question of how he even knows the difference to begin with...
 * Played with in the "Thanksgiving" trailer in Grindhouse, when two small-town detectives are investigating a murder scene amid the titular holiday parade:
 * Cop 1: (Touches, then tastes) "It's blood." Cop 2: "Son-of-a-bitch!"
 * It should be pointed out that by "investigating a murder scene" we mean, "The headless body is right there and the blood is still leaking out of it".
 * Star Trek VI: The Undiscovered Country: Chekov finds a dried drop of something pink on the transporter pad, and pokes it before taking a sample. It's Klingon blood, which is what he was looking for.
 * Repeated in the director's cut, with Colonel Worf investigating the pool of blood surrounding the attempted Klingon assassin.


 * Actually somewhat justified in Cornered, since a lot of shelves were knocked over, and it could have very well been ketchup.
 * The 2001 obscure Nickelodeon movie, "Snow Day", had the elementary students try to derail the snowplow man's efforts to remove the snow from the streets since it will reopen their snowed-in school. One of their less successful methods was having one of the students lie in the middle of the street in wait of the snowplow man with ketchup on his shirt pretending to be unconscious. Bemused, the snowplow man simply stands next to the boy, dipping his frenchfries in the ketchup and eating them.

Literature

 * In Robert A. Heinlein's To Sail Beyond the Sunset, the protagonist wakes up in a strange hotel room with a dead body in a pool of blood. After she phones for help, two doctors arrive. They each dip a finger in the "blood" and taste it. As she is feeling rather sickened, they begin arguing over whether it is Heinz or Hunts brand ketchup.
 * In Chris Jericho's autobiography A Lion's Tale, he describes a Ketchup Test incident that occurred during one of his early matches. Jericho bled a lot in this match and one of the ringside fans, believing Jericho's real blood to be ketchup, dipped his finger in a pool of Jericho's blood and put it in his mouth.

Live Action TV

 * Dave Chappelle explains that since semen is also a tool used by police to frame the black guy while doing their jobs, they might check that instead.
 * Though it wasn't blood that he tested it with, Gil Grissom did this twice in CSI. The first time, Brass merely stared in horror at him; the second, Catherine warned him how unsanitary it was.
 * In an episode of Fringe, the ketchup test is notably Averted. The team finds a reddish stain on a piece of evidence left at a kidnapping scene, believing it at first to be blood, but they bag it and submit it for analysis only to discover that it is not blood but hot sauce.
 * Walter has a recurring habit of tasting whatever disgusting thing they're dealing with and then revealing it's just some food he left lying around in the lab. He's done this with what appeared to be blood, brain matter, and cremated ashes. Taste is apparently the most important sense for scientists.
 * Given that, the hot sauce example seems particularly notable, since it would be a perfect specimen for Walter's Sniff Sniff Nom antics, since hot sauce generally has a distinctive odor.
 * The Doctor does this in the Doctor Who episode "The Christmas Invasion". He then tastes the blood and identifies it as "A-positive, with just a hint of iron" (Although his Bizarre Alien Biology could let him do this).