Poisons in detective novels are one of the great romances in fiction. Writers of the genre are always looking for new ways to administer the deadly stuff, which gives us this trope: a murder method wherein poison is unwittingly self-administered when the victim licks an object coated in the poison.
The object could be anything, although the more innocuous, the better. One popular method is to coat the pages of a book in poison, so that when the victim licks their finger to turn the page, the poison is passed to them. This is somewhat dated, since people don't lick their literature much anymore, but it may be Justified by saying the pages were stuck together or from an old, delicate book.
Other seemingly innocent lickable objects, such as stamps or envelopes, are also popular.
Related to, but separate from, Poisoned Weapons and Drugged Lipstick. The murderer may use a Perfect Poison to do the job. Not to be confused with a Fingertip Drug Analysis, though less-subtle examples may rely on the victim trying one.
Finger-Lickin' Poisoned Books:
- Diabolik once used this method, soaking with cyanide the text of a speech a journalist would later read to call Ginko an incompetent and Diabolik himself a lousy criminal. Diabolik chose this method specifically because he knew the journalist had this habit and wanted to kill him in a most spectacular fashion.
- In Red Robin a member of the League of Assassins kills a witness, and the bailiff as collateral, by poisoning the courtroom Bible she is to put her hand on to swear in.
- The Internecine Project ended with the murderer receiving a hand-written notebook from one of his victims. On the last page it said "I arranged for this to be sent to you after I am dead, and the pages have been soaked in poison that is absorbed through the skin".
- The Name of the Rose: In an attempt to keep Aristotle's Poetics hidden, an evil monk poisons the page corners so anyone who reads it will die before they can tell others about it.
- In The Island of the Day Before, Eco mentions it again as a Production Throwback.
- Older Than Print: The Arabian Nights tale The Tale of the Vizier and the Sage Duban, wherein the Duban, sentenced to execution by a treacherous king, gives him a book with orders not to read it until after his head has been cut off. After that's done, the head comes back to life and instructs the king to turn three pages with his left hand. When the king turns the pages (naturally, licking his finger along the way) and finds nothing written there, the Duban essentially tells him the pages were poisoned and if the Duban had to go, he was taking the king with him. Crowning Moment of Awesome for a severed head. (Unfortunately, this makes the vizier who caused the execution a Karma Houdini, as he didn't touch the book and sure as hell wouldn't after seeing what happened to his king.)
- In the Discworld novel Feet of Clay, this is one of the theories as to how Vetinari got poisoned, in an obvious shoutout to The Name of the Rose.
- This technique is mentioned in Bridge of Birds, with the added element that the books in question were pornographic.
- Classic example: in Alexandre Dumas' La Reine Margot (AKA Marguerite de Valois), a poisoned book is used in attempt on King Henry of Navarre's life, but the plan backfires with disastrous results. Earlier in the same novel, an even more devious plan to poison Henry via his paramour's lipstick is employed but thwarted by the would-be poisoner who couldn't murder said paramour in cold blood.
- While it isn't poison, per se, in Red Seas Under Red Skies, the two Gentlemen Bastards use this as a way to cheat at an uncheatable casino. They're playing cards against a pair of women, one of whom is known to eat chocolates and lick her fingers as a part of her mental game to throw off her opponents. So they dust their suit linings with a powerful sleeping drug so they can keep coating the cards with it. This works especially well since the game also requires that whoever loses a particular hand must down a shot of liquor, with the losing team being the one that has one of its teammates pass out.
- In Murder and Mendelssohn, a conductor who habitually licks his finger before turning the pages of his score is poisoned when the killer coats the top of his score with arsenic.
- In Guy N. Smith's apocryphal Sherlock Holmes story "The Case of the Sporting Squire", Royston Morgan (aka "Morgan the Poisoner"), knowing his wife is in the habit of licking her fingers each time she turns a page, kills her by adhering strychnine to the pages of Little Dorrit. She dies alone in a locked room, as he hoped, and the local doctor passes the death off as tetanus, but neither Holmes nor Watson are so easily fooled.note
- 11th Hour used this one early in its first (only?) season.
- The pilot of Crossbones has Tom Lowe using this in attempt to assassinate the pirate Blackbeard. It almost works, but Lowe is forced to reverse the effect when he discovers discord among Blackbeard's underlings, and needs to keep him alive to better investigate it.
- In the CSI: NY episode "Page Turner", the killer coats the pages of a book in thallium to poison his victims.
- Ellery Queen: The murder method in "The Adventure of Caesar's Last Sleep".
- Death in Paradise has done this twice. In the first case, it was stamps, and the twist was that the murder was based on knowing the victim's habits, allowing the murderer to be flying on an airplane at the time of the murder. In the second, it was an envelope, and the twist was that the dose had been low enough to be slow-acting, allowing the murderer to be conveniently away and then return when the victim collapses to plant a much higher (and therefore fast-acting) dose in the victim's champagne glass, making it look as if the victim had been poisoned in a very short gap of time for which the murderer had the perfect alibi of being nowhere near.
- In the first book of the Grimtooth's Traps series by Flying Buffalo had an 'additional trap', to 'punish' players who read the book. On the trap page, Grimtooth claimed that the book pages had been liberally coated with a deadly neurotoxin absorbed through the skin ... with two blackened fingerprint outlines right where a normal reader would hold the book when reading.
- In the old TV show, Jacob Two-Two, a bad guy puts into motion a plot to kill people via this method. He fails
- It wasn't murder he was after; he wanted to brainwash them into buying his products. He failed because the titular character and his best friend didn't lick their fingers while reading and so were able to figure out his scam.
Other Lickable Objects:
- In Detective Conan, a man was murdered via poison applied to the temperature control of a cooking range on which a pot of water was boiling, after which he counted money and licked the poison from his fingers.
- One of the movies had a woman murdered in a similar way. her make-up artist put the poison in her make-up, and then gave her normal chocolates on an airplane trip. The woman pinched her nose to pop her ears, getting the poison on her fingers, and then ate a chocolate and licked her fingers, ingesting the poison.
- Another example: a musician is murdered by poison applied on the inside of his jacket sleeve and asked to perform a song that required him to throw off the jacket and take a pose where the poison would transfer to his hand. The food, all non-poisoned, were things like sushi and nigiri and there were no eating utensils.
- Another man was poisoned via a poisoned wet napkin while eating sushi.
- And YET ANOTHER was poisoned because his murderer put poison on the spot on the lazy susan between two dishes that the victim was allergic to, and so he kept getting poison on his fingers every time he saw said dishes.
- A man who disliked sour things was nevertheless poisoned by a lemon wedge in his drink because, as part of a marketing gimmick, he had eaten a miraculin berry and was unable to taste the sourness.
- Even detectives aren't immune to this trope! He died biting his nails, not realizing that his partner had betrayed him and poisoned everyone's cup handles except for her own.
- One Batman comic featured the Joker's venom being applied to postage stamps. The twist being that the Joker didn't do it.
- In the classic "The Judas Contract" storyline in Teen Titans, Deathstroke captures Gar 'Changeling' Logan by drugging the gum in the envelopes Gar is using to respond to his fan mail.
- In Red Robin Funnel kills a member of the League of Assassins by poisoning the crucifix she knows he always kisses after completing a kill.
- In Discworld stamp-collecting, the original Assassins' Guild 3p stamp (the Thrupenny Dreadful), is very rare, at least gummed. The in-universe reason for this is that they were recalled due to unsubstantiated rumours that the Guild was using it to fulfill contracts.
- In Robin Hobb's Assassin's Apprentice, one of Fitz-Chivalry's assassination ploys was to poison the cutlery instead of the food.
- During the Mallorean series, Sadi kills a man by coating the man's soup spoon with poison.
- A Song of Ice and Fire: twice, with the same method. First the prologue of A Feast for Crows: The Alchemist (Jaqen H'ghar's new personality) pays Pate, a novice in the Citadel with a poisoned coin. Pate bites the coin, then the dust. Second, Arya's first sanctioned killing in Dance: she deliberately botches a cutpursery to replace one of the coins of a ship owner with a poisoned one. The owner then pays a greedy insurer with said coin. The insurer also has a habit of biting the coins....
- The Three Widows, by Ellery Queen had a victim being slowly poisoned even though everything she ate and drank was carefully screened beforehand. It turned out the would-be killer was her doctor and the poison was on the thermometer with which he took her temperature each day.
- Non-poison example: In Red Seas Under Red Skies, Locke and Jean win a card game by sprinkling a sleep-inducing drug on the cards. One of their opponents is notorious for eating and licking her fingers while she plays, and she forfeits the game when the drug puts her to sleep.
- Joe Pickett: In In Plain Sight, J.W. Keely murders a prisoner by smuggling him a can of chewing tobacco laced with cyanide. He hopes that the prison guard who probed the tobacco with his finger doesn't lick his fingers afterwards.
- The Thinking Machine: In "My First Experience with the Great Logician", the narrator accidentally poisons himself by smoking a cigar he stored in a jacket pocket where, several months earlier, he had carried a packet of insecticidal powder. Some of the powder had leaked and coated the tip of the cigar.
- There was a Remington Steele episode where the poison was in the glue on some envelopes Steele and Laura were expected to lick.
- In Seinfeld George's fiancee is accidentally poisoned by the cheap glue on the wedding invitation envelopes, because George was too stingy to pay for better ones (and too lazy to seal any invitations himself).
- And Susan herself was too stupid to use a sponge rather than lick the envelopes herself—-poison or not, those seals taste terrible.
- In the Jonathan Creek episode "The House Of Monkeys" the victim was sent a request for a signed copy of his book. The murderer included a stamped addressed envelope to send the book in... stamped, addressed and poisoned with a psychotropic drug on the flap you lick.
- During the course of an attempted murder, the apparent victim spilled ricin on her pen, and then killed herself by biting the end of it. This isn't actually possible, as while injected ricin kills in very small doses, a human body can survive ingesting nearly a whole gram of it.
- One episode involved poison-laced nail polish.
- In the Criminal Minds episode "Poison," the team discovers that groups of people who had been slipped LSD had ingested it by licking bank envelopes whose seals were coated in the drug. Later in the same episode, the UnSub tries to poison a group of people with botulism via the same method.
- In one episode of Benson, a person with a habit of sucking on the earpiece of his reading glasses was killed by poison placed on the earpiece.
- The stamp variant occurs in a series 3 episode of Death in Paradise: the murderer knows that the victim writes postcards each time she lands somewhere new, including licking stamps to send them, and uses this knowledge to poison the stamps and thus the vic. And in doing so gets an alibi since the actual death occurs on the ground while the murderer is still on an aeroplane en route.
- In an old Perry Mason episode, it turns out the murder weapon was poison on a brooch and a dress with no pockets. The murderer was the dress designer and the victim was the model picked to show off the dress in question. The dress was designed to wrap around the wearer in a complicated way that required both hands to accomplish, and then be pinned closed with the brooch. Since the dress had no pockets, of course the model put the brooch in her mouth while tying the dress and got a lethal dose of the poison. The murderer tried to cover up the method by putting more poison into the bottle of champagne used to toast the success of the fashion show, but of course Perry saw through that one.
- Father Brown:
- In "The Time Machine", one victim was killed by having strychnine placed in the bowl of his pipe.
- In "The Wrath of Baron Samedi", a musician is murdered when the killer coats the reed of his saxophone in poison. The killer later dusts Father Brown's toothbrush with the same poison.
- Death in Paradise:
- In "Damned If You Do...", the Victim of the Week if poisoned by a lethal dose of poison being placed on the end of his pen before he retires to write a speech. The killer then poisons the dinner being eating by everyone, including themself, with a milder dose in an attempt to make it appear he died from food poisoning.
- In "One for the Road", the killer gives the Victim of the Week an envelope with a poisoned seal, knowing that the victim will lick the envelope, seal it and place it in her bag. Then, after she dies, the killer doses her glass with poison to make it look like she had drunk it.
- In the Pathfinder adventure path Curse of the Crimson Throne, the King of Korvosa is killed this way, setting the entire plot in motion. The poison was placed on playing cards, and the king is a habitual nail-biter.
- A poisoned letter stamp in Apollo Justice: Ace Attorney. Also upgraded to poisoned nail polish, because the intended victim, a young girl named Vera Misham, had a tendency to bite her nails a lot.
- A Game at Dinner, an in-game short story in some Elder Scrolls games, has Helseth implying to his assembled dinner guests that he put poison on the cutlery of someone he knows has been spying on him. It turns out to be a subversion, however, as Helseth was Bluffing The Spy, and the real poison is the antidote he offers to the spy if they confess.
- Finger-licking isn't explicitly mentioned, but in Assassin's Creed II, Agostino Barbarigo dies after receiving several poisoned letters from the Assassins.
- In Aviary Attorney luxury chocolates with a custom wolfsbane-derived filling are so poisonous that a character who eats the wrapping which has traces of chocolate on it is hospitalized.
- While not highly toxic by itself, Dimethyl Sulfoxide (DMSO) has the property of being quickly and easily absorbed through skin contact, allowing easy contact absorption of whatever else happens to be mixed with it. This allows a deadly but hard to deliver poison to be easily absorbed through the skin. It is regularly used as a solvent in industry and scientific research, so it's quite easy to get hold of too.