Writing Indentation Clue
When people write a letter or a note, it's possible that the pressure of their pen or pencil will create indentations not just on the paper they're writing on, but on any paper that's underneath it, too. In some sorts of story (particularly Mystery Fiction, though not exclusively), making use of this fact is a well-established investigative technique. If you want to know what someone wrote on a notepad but the note is no longer there, just look at the next piece, possibly shading it with a pencil to bring out the contrast. In certain genres and at certain times, this trope has been common enough that a Dangerously Genre Savvy villain might take steps to avoid it, such as by taking several sheets from a notepad, or slipping a piece of cardboard between the top two sheets, to prevent the pesky detective from doing this. A number of variations on this exist—for example, it isn't always paper that the indentation gets made on. A similar concept from the time when writing involved a lot of wet ink was to look at the blotting paper (used to absorb excess ink). Carbon-copy and triplicate-copy paper are designed to take advantage of this, allowing the impression to release ink so that multiple copies are written or typed at once.
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Anime and Manga
- Detective Conan uses this method to gather clues occasionally.
- In Death Note it becomes vitally important in the final storyarc. Light has had the Death Note for so long, using it to become the mass-murderer (and in his mind, Living God) "Kira" (Killer), and been able to successfully dupe for so long the police team that he's a member of which is meant to hunt Kira, that he gets, well...overconfident and sloppy. He has meetings with one of his new catspaws, which he realizes are being recorded by hidden microphones, so he has seemingly normal conversations with her in their hotel room, while passing her hand-written notes giving his real Kira-directed instructions. Unfortunately for him, his police colleagues finally grow suspicious of him - well, he was always one of the top suspects to be Kira, but he managed to trick them with so many fake alibis that they had long since written him off as a red herring. At any rate, one of them later goes into the hotel room he was in, and uses the writing indentation clue on the notepad he was writing instructions to his agent on — Light grew so overconfident that he stupidly forgot about this little trick entirely. While the actual content of the indentations wasn't particularly damning, the fact that he was trading secret messages instantly tipped them off that he'd been throwing up smokescreen misdirections, a red flag that he actually was Kira.
- In North By Northwest, Thornhill is able to figure out where Eve is going by finding the impression of an address she wrote.
- Subverted in The Big Lebowski: The Dude uses this trick to see what Treehorn wrote while taking a phone call, but it turns out to be just a doodle of a man with... implausible anatomy.
- Wild Wild West. Dr. Loveless writes down information about the rendezvous point on a piece of paper and gives it to Bloodbath McGrath. Jim West uses this technique to discover where the rendezvous point will be.
- In M the child-murderer writes a letter to the newspaper, using a single sheet of paper, a pencil and a wide windowsill in his apartment as a desk. When the police raid the apartment, they find a partial impression of the words in the letter in the wood. In this case, they already knew what had been written; the indentations were, instead, proof of who had written it.
- Used in Cloud Atlas to figure out the address of a murdered scientist's daughter.
- The Russia House. The protagonist is taught to write on a glass surface to avoid this trope. He later does so, using a picture taken off the wall.
- The Fourth Protocol is about a Soviet plot to detonate a nuclear device on British soil and Make It Look Like an Accident. As such an act violates a secret protocol between the nuclear powers, various people get bumped off because They Know Too Much. A female military scientist is sent to assemble the bomb that the KGB agent played by Pierce Brosnan will detonate. She delivers a message which Brosnan decodes using a one-time pad, then he burns the message claiming that it just confirms her instructions re setting off the bomb. She ends up sleeping with him, and the morning after rolls over in bed and sees the imprint on the notepad: KILL HER. Brosnan immediately shoves a pillow against her chest and fires his gun through it.
- Strings shakes it up a little, when its inadvertent usage implicates Nezo.
- In the Mexican film La Habitacion Azul, this is how the cop of the movie discovers a message Andrea sent to her lover after her husband died, saying "Now it's your turn"; he uses it to accuse Andrea of murdering her husband and egging her lover on doing the same with his wife.
- In the novelization of Gabriel Knight: Sins of the Fathers, when Gabriel discovers that Professor Hartridge is dead, he also finds that the office has been picked clean of evidence, including some notes the professor had been working on to help Gabriel. Fortunately there's enough indentation left in the sheets underneath the removed notes that Gabriel is able to use a pencil to employ this trope to find out what the professor had written anyway. (In the game itself, Gabriel is able to just take the notes without having to go through all that.)
- Mentioned by Sherlock Holmes when telling Watson how he got his information as "a fact that has dissolved many a happy marriage". However, in this case he uses the blotting paper to obtain the reverse message, as the writer had used a pen.
- In Les MisÚrables, Valjean discovers Cosette's letters to Marius by looking at the blotting paper.
- Agatha Christie probably has many examples, but there's definitely a Miss Marple short story. Very shortly before his well-off wife dies, a man writes a letter; the rather suspicious phrases "hundreds and thousands" and "when she is dead" are picked up from the indentations on the sheet underneath. The man, however, explains that he was writing a reply to his brother, who had asked for money; whilst he would have money after his wife was dead, he had none currently, and that hundreds and thousands of people were in the same boat. He's lying.
- The psychokinetic children in From the New World are given their own mantra and told to keep it a secret, but the heroine was curious enough to persuade her classmate into writing down his mantra and giving her a glimpse of it. She couldn't see it clearly, of course, but she read it by shading the sheet underneath with a pencil after he left.
- In Bulldog Drummond, a mook assigned to trail Drummond uses this to find out what Drummond wrote in a telegram—but reveals a rude message from Drummond, who'd realised he was being followed.
- Mentioned briefly in the book version of The Time Traveler's Wife; this is how Clare discovers Henry's intention to get a vasectomy.
- Played with in Jingo, part of the City Watch subseries of the Discworld books. Someone had written a note on a pad of paper, but someone else came along and took the next few pages to prevent anyone else using this technique. Vimes addresses the resultant Fridge Logic: Why didn't he just take the whole pad? Because he also wanted Vimes to be curious about the contents of the note.
- The Dresden Files: In Death Masks, Harry Dresden recovers a thief's notepad after seeing her tear off the top page. He shades the page underneath it with charcoal to find out what she'd written.
- In Death of Achilles, Fandorin figures out the bad guy's address by tracing the indentation in a notepad he found on the scene.
Live Action TV
- In an episode of Lois and Clark, Clark uses his powers to read several messages indented on a wooden desk.
- In the Eureka episode "Before I Forget", Carter uses this technique on his ticket book in order to learn the license plate number of the last car for which he wrote a ticket.
- Found in an episode of Shark with two variations: the first being that it's not a text, but a drawing, the second that the detectives don't use a pencil to bring it out, but a computer.
- In an episode of Ashes to Ashes, Alex Drake uses a pencil on Super Mac's Diary to uncover a secret meeting between him and a murder suspect.
- An episode of CSI NY has the motive revealed by this type of clue in the Body of the Week's notebook. The victim had discovered a dextroamphetamine abuse epidemic in his high school and was going to blow the whistle on it to The New York Times.
- In an episode of Monk, "Mr. Monk Takes His Medicine," Monk suspects that something is wrong with suicide victim Marlene Highsmith's suicide note. At first, he doesn't seem to know or care what is wrong because he is on Dioxynl, but when Monk goes off the drug, he realizes that the note was not Marlene's because it was written with a red pen, and there is no red pen in the kitchenette the note was written in. Monk takes the writing tablet the note was written on, and uses chalk rubbing to reveal Marlene's actual suicide note - a confession that her ex-husband Lester Highsmith is staging an armored car robbery, that happens to be going down right at the moment Monk and Sharona discover the note. Lester had written the suicide note the police found and staged a drive-by shooting a few blocks away to keep the cops away while he switched out notes.
- In Elementary, a piece of newspaper is found at a bombing that killed two people. A word was found indented on one of the pieces of newspaper used to make it and the handwriting on it was matched to the bomber.
- Columbo: In the episode "Now You See Him", the Great Santini shoots Jesse Jerome immediately after Jerome types a letter exposing Santini as a wanted war criminal named Sgt. Stefan Mueller. Columbo catches Santini by examining the typewriter ribbon, which contained an impression of all the keys the victim had pressed.
- In Angel, when Cordelia's missing, Angel suggests trying this with her memo pad to see what the last message she wrote down was. Gunn counter-suggests checking the carbon copy.
- NCIS: McGee is a writer who still uses an old-fashioned typewriter. A Loony Fan steals his used typewriter ribbons and commits murders inspired by the plot.
- In the season six premiere of White Collar, Neal uses indentations and carbon paper to tip off Peter of to the fact that he's targeting the crime syndicate Pink Panthers, while his kidnapper and captor looks on and even checks to make sure Neal isn't passing messages.
- Used by Lee in one episode of The Walking Dead to get instructions for how to drive a train from a ripped notepad.
- Cole uses this trick to gather evidence for a few cases in L.A. Noire.
- Deadly Premonition: York uses this to find the contents of Becky's secret diary.
- In Dangan Ronpa, this is used in solving the first case, as there was a note passed between the culprit and victim.
- In Season of Mystery: The Cherry Blossom Murders, this provides evidence of what (and who) the protagonist's husband had been looking into before his alleged suicide.
- Used in Scratches, when Michael reveals a letter from the former maid of the mansion to her family, in which she details her account on the events that happened in the mansion and revealing the location of a secret compartment.
- In the Creepy Pasta Easter Egg: Snow on Mt. Silver, the sister learns the redacted GameShark code by holding the paper up to a light to see the indentation.
- Phineas and Ferb has Candace use this when she and Stacey are trailing the boys in England, referencing Sherlock Holmes when they find a notepad with half a page torn off. Candace shades the page underneath to reveal the full message and the location of Phineas and Ferb.
- An old episode of Scooby-Doo has Fred, Velma and Daphne come across someone's diary whilst looking for clues. They find that the ink of the text has faded, but the pressure of the pen has worn through to the next page. So one of them grabs a coal and shades the paper to see what was written.
- In The Little Rascals episode "The Case of the Puzzled Pals", Alfalfa and Darla find such a clue via pencil rubbing on the notepad Spanky used in taking a call from his mother.
- Used as a real technique by police, should the circumstances happen to suit it. There are machines called electrostatic detection devices which are able to do a considerably better job than the pencil-rubbing method.
- In many typewriters, the ribbon will have the shape of the letters typed clearly visible where ink was pushed off for the letter that was printed. Unrolling the ribbon would allow someone to see what's been typed.
- Queen Elizabeth II apparently uses (or used, given that modern writing implements made it obsolete) black blotting paper to avoid that variant of this trope.
- There tend to be strict regulations against using any surfaces allowing that when composing secret documents.