"Encyclopedia Brown? What a hack! To this day, I occasionally reach into my left pocket for my keys with my right hand, just to prove that little brat wrong."
This is a specific kind of Did Not Do the Research, where a pivotal clue in solving a mystery or puzzle is actually erroneous. This is related to Conviction by Contradiction, where a single thing wrong with an alibi is sufficient to prove guilt, but goes further: the key that makes the claim or alibi wrong is itself factually incorrect.
For example, a guy's alibi is that he was caring for his pregnant mule, and he is immediately revealed to be lying, since mules can't get pregnant. We've got him! To the jail! Not so fast: while they're rare, fertile female mules do exist; a mule's foal is precisely what the picture to the right depicts (one also has to wonder why no one ever asks to see this newborn if it's someone's alibi). Thus, there's a problem with this "revelation": it's simply wrong.
Distantly related to Dan Browned, because if you're going to write a mystery and have the solution all hinge on one fact, the audience is fully justified in expecting that that fact is really a fact.
When adding examples, keep in mind that a fact has to be actually wrong to qualify for Conviction by Counterfactual Clue. If there's simply a way to explain away the objection without calling factual rightness into question, it's Conviction by Contradiction. Many examples, especially ones with complex contexts, have some aspects fall into one, and others into the other.
This can be sometimes excused by Science Marches On. In many cases, the "clue" started out as Conviction by Contradiction, then science marched it right over here. When this happens but the ultimate conclusion is demonstrated to be correct, it overlaps with Right For The Wrong Reasons, especially when other clues in the story are skipped over, but are both factual and more useful.
Oh, for the record, it's male mules that are always infertile— but then the "clue" wouldn't work at all.
The "mule" clue was used in "The Case of Molly's Mule."
A Two Minute Mystery had a deaf witness's testimony that he read the suspect's lips and took special note of it because the suspect was whispering called into question, because supposedly, he shouldn't have been able to tell the suspect was whispering. However, whispering is more than simply a matter of volume, and does look different to a lip-reader.
In one, Haledjian asks for bicarbonate of soda for an upset stomach while in a bakery that produces only fruit pies. The baker says she doesn't have any; this leads the detective to deduce that the bakery must be a front for smuggling, since bicarbonate of soda is baking soda and no real bakery would be without it. But fruit pies don't require baking soda! While there are recipes for fruit fillings and for pie crusts that use baking soda, most don't. There is also the possibility that the baker was unfamiliar with the scientific term for baking soda.
In one Two Minute Mysteries story, a man relates how he leaned over his train bunk and read a headline on the newspaper the man below him was apparently reading. His companion deduced that the man with the newspaper was the perpetrator, because the only way the first man could have read the headline is if the newspaper was held upside-down (and therefore upside-up, relatively speaking, to the first man's eyes.) However, many people can read upside-down text just fine, especially if the text is in a large font and the message short—for example, the text of a headline.
The page quote comes from a mystery where one kid with a cast on his left arm is accused of stealing some keys, and in fact they're found in his pants pocket in his locker. However, the "proof" that he didn't do it is found in that the keys are in his left pocket, and, according to Encyclopedia, it's impossible to put keys in the opposite pocket of the hand they're in while running, as Bugs Meany claims happened. It might be more difficult for some than others, but it's certainly not impossible for everyone.
In one case, the culprit's alibi was that, when he walked past the victim's house, he heard the electric clock (which was unplugged when the crime was committed) ticking, the contradiction being that electric clocks don't tick. For the sake of expediency, we'll ignore questions like "how loud would it have to be ticking to be audible outside the house?" and "exactly how is this an alibi anyway?" and skip straight to the fact that some electric clocks — particularly analogue clocks in which the second hand jumps from one mark to another and an early kind of digital clock where numbers were written on flaps that showed in succession (as shown in Groundhog Day among others) — do make sounds that, while distinct from pendulum-regulated clocks, are described as "ticking". Additionally, some digital clocks that indicate seconds will play an artificial ticking sound.
One involving a sword from The American Civil War. The guy hawking it claimed it was authentic due to the engraving showing that it was given to Stonewall Jackson by Robert E. Lee after the First Battle of Bull Run. The 'correct' answer was that the sword was fake, because nobody would have called it FIRST Bull Run until there had been a Second Bull Run. Given how long it can take to commission, make, retrieve, and engrave a sword, it's entirely possible that the second battle a year later either already happened or was soon coming, necessitating the need for specificity.
Improved slightly in a reprint of the story by pointing out the much more useful fact that the Confederates always referred to the battle as the Battle Of Manassas, not Bull Run. The reprint also changes the inscription from "Presented by General Robert E. Lee" to "Presented by his men", since Robert E. Lee was neither Commander of the Confederate army, nor anywhere near Manassas at the time — he was in western Virginia, and wouldn't assume command for over a year after the battle. (Had Jackson been awarded a sword after the battle, it would most likely have been Joseph E. Johnston doing the presenting.)
Encyclopedia Brown pinned a crime on a magician because he was wearing short sleeves. He claimed that all magicians wore long sleeves so that they could pull objects out of them, when many good magicians don't need anything of the sort. Many, in fact, wear short sleeves solely to impress people with the undeniable fact they have nothing up them, and at least one performs magic in the nude. There are entire styles of magic that depend on (for example) marked cards, psychological tricks, or props with trap doors, for which sleeves are completely useless.
Worse still: pick up a magic trick guide book, any one. You will not find a single trick that relies on the magician using sleeves.
One case was "solved" (by Sally, not Encyclopedia) because a couple sat in a restaurant with the man's back to the wall rather than the woman's, from which Sally deduced that each was actually a member of the other gender in disguise. This is because of a rule of etiquette that the woman should sit against the wall, so she can see and be seen. For this to be evidence, it would have to be the case that people followed this "rule" with no, or at best very few exceptions; but even putting aside the fact that people from some places don't observe it at all, even in areas where it's well-known it's violated all the time.
Worse: either the couple knew about the rule, but then for what reason should they sit according to their real gender instead of their disguise, or the couple did not know the rule, in which case their sitting order was totally random. Either way, nothing can be deduced, except that a couple sitting in the "wrong" configuration is more likely to not know the rule.
Another point on this is that the rule is fuzzy anyway, as another form exists: the man should sit in such a way as to see the most of the restaurant so that he can perceive any dangers and act accordingly (protect the woman), especially in unfamiliar locations.
Another solution was based entirely on the supposed 'fact' that roosters only crow when they saw light (the crime was a con man trying to convince kids he found a way to make roosters crow on command, and he claimed that soon they would find a way to make them lay eggs on command). Now, anybody who has been around a rooster for an extended period of time will know full well that they crow whenever the heck they want, whether the sun is out or not.
One solution in Encyclopedia Brown Takes the Cake relied on the fact that the culprit had used glycerin tears that fell from the outside corners of her eyes instead of the inside, thus revealing them to be fake, as "If only one tear falls, it will run from the inside corner of the eye, by the nose, and not from the outside corner." Only, none of that is true.
In the Sherlock Holmes story "The Adventure of the Priory School", Holmes deduces which way a bicycle was traveling by the way the tracks overlap. His description doesn't actually work: the overlap tells you which wheel left which track, but not which direction the bicycle was going. In the "New Annotated Sherlock Holmes", the story is followed by two pages listing various attempted retcons for the error. Not quite as bad as it seems at first glance, as some particular kinds of turns will have the turn start with the front wheel flicking to the outside of the turn to induce the lean needed to accomplish the turn. Ends of turns almost always have smooth rejoinings of tracks.
It is actually possible to deduce which way a bicycle is going through the tracks of a turn; it has to do with the fact that the rear wheel always points directly towards the front wheel in the direction of travel.
You could also be generous and say that in riding a bicycle over rough ground, as in this story, there will be times where the wheels leave the ground which would help enormously.
Another Sherlock Holmes example: in "The Adventure of the Blue Carbuncle", Holmes deduces that the owner of a lost hat must be an intellectual, because it is a big hat, and so he has a large head. Again, it's largely Science Marches On; that was actually a serious scientific theory at the time.
In a Mike Mist Minute Mystery by Max Allan Collins in the early 1980s, the title character supposedly identifies a crook because she claimed that she cashed a check using an automatic teller machine, which Mike claims is impossible. Here, the readers wrote in to note that it's done all the time; you enter the correct amount of the value of the check into the machine as a deposit and you are free to withdraw from that amount. And of course, Technology Marches On: you can now deposit a check into (some) ATMs, and the machine is sophisticated enough to scan it and correctly parse the writing as a check amount.
One entry in The Armchair Detective series stated that one true way of knowing if a pre-World War II telegram is false is if the phrase "World War One" or "The First World War" is ever mentioned, on the assumption that nobody could have foreseen a second World War before it started. However, it was used by some almost immediately after hostilities began. Note that the series in general isn't particularly prone to this. In his defense, those were not common terms, and would hardly be included in a telegram where they could easily say "The War" or "The Great War" with fewer letters. It may not be rock-solid evidence, but it's a good reason to be very skeptical.
It should be noted that using them as the actual name of the War would be even more suspicious - although the First World War was, indeed, used, it at first was more of a descriptive term (IE, describing the War as the first World War in contrast to previous, non-global, wars, and, as in the case of the first recorded use of the term, the early-war term 'The European War').
This is Science Marches On rather than Did Not Do the Research, but one of Isaac Asimov's space mysteries hinged on the fact that one side of Mercury always faces away from the sun, because at the time it was reckoned this was true. Later research proved this wasn't the case, which Asimov acknowledged once he learned it — unfortunately, he couldn't see any way to amend this clinching evidence without completely re-writing the story.
In the MonkTie-In NovelMr. Monk in Outer Space, one of Monk's deductions hinges on the fact that insulin must be refrigerated. Except it doesn't; diabetics commonly keep vials of insulin currently in use at room temperature, usually due to the discomfort of injecting cold insulin. He also incorrectly states that all diabetics take insulin, when some Type 2 diabetics can control their diabetes through diet and exercise alone, and most can control it with the help of oral medication.
Refrigerating insulin mostly has to do with preserving it longer. Doctors recommend keeping insulin at room temperature for a month at most, while keeping it cold extends this to six months.
One Encyclopedia Brown-esque story concluded that the suspect was obviously lying because he claimed he was at a laundromat putting clothes into a top-loading dryer. The detective claimed that all dryers are front-loading. This is incorrect; top-loading models existed on the market even in the time period when the story was written.
This happened with Encyclopedia Brown himself. Bugs Meany lied by copying another kid's true version of events, changing washer to dryer but otherwise using the exact same words. The first kid said he'd put the clothes in from the top, and Bugs copied that detail.
The vital clue that solves the mystery in the novel Fatal Equilibrium doesn't work at all once the Fridge Logic sets in. Canoes would necessarily have a smaller price variance only if one assumes all canoes are the same, which is a bad assumption to make when applied to non-theoretical situations. This is even worse when the protagonist makes the comparison of a hammer and a car. Anyone with half a brain would realize that, while the price variance of a specific make and model of car would likely be smaller than that of a hammer, cars in general have a considerably larger variance due to differences in performance, fuel efficiency, mileage, current fads, etc. This effect could actually be even more pronounced in the society under question, which did not have mass production, meaning each canoe would be unique.
In the battle between Archmage Gromph and Dyrr the lich in the War of the Spider Queen series, Gromph realizes Dyrr's shapeshift spell means he's not undead anymore, so negative energy spells can and do work on him. The kicker? He'd polymorphed into a construct, which is still immune to negative energy and a Lich, unlike most undead, CAN polymorph himself as an explicit part of the runes.
Woody Allen parodied this in a story called "Match Wits with Inspector Ford", where Inspector Ford deduces that a man didn't kill himself, because there was cash in his pocket, and someone who is about to commit suicide would use a credit card.
There was this one story where someone said they saw a thief in their house because they held a spoon up and could see the reflection. This was outed as spoons show reflections upside down. I mean, obviously you can't tell it's a person from an upside down image. That'd just be silly. There's also the tiny detail that reflections are right-side up on the back side of the spoon!
Comic Books
In the 1980s and 1990s, the Swedish edition of The Phantom had a page of reader-submitted material, of which one of the more popular were crime mysteries (see Conviction by Contradiction for more details). One of these had the culprit give himself away by referring to the banana as a fruit. Even though banana trees are herbaceous plants, a banana is biologically considered a fruit. Even when using the culinary term for fruits (which is probably the term most people outside of the fields of biology, botany, and horticulture are familiar with), this still doesn't exactly excuse the conviction, as the banana is one of the most classic examples of a "Culinary Fruit." (For a more specific description, a culinary fruit is any edible fruit that is sweet. Biologically, a fruit is a plant structure that contains seeds. This is why things like tomatoes, peppers, eggplant, and cucumbers are classified as fruits by botanists, but not by chefs.)
The trope is invoked and lampshaded in Welcome to Tranquility. Emoticon is in jail and being questioned with regards to the murder of Mr. Articulate, a crime-solving member of the community who was legendary for his intellect, wit and long and storied history of traveling the world. However, Emoticon points out that a lot of the stories of his adventures were "culturally insensitive", and he recounts one of the detective stories from Mr. Articulate's youth that always stuck in his mind: Mr. Articulate discovered the identity of the murderer because the "Korean" man at dinner left his chopsticks in his bowl of rice, something no actual Korean would do since it is a symbol for death and, therefore, he must not be Korean, but Japanese instead, and thusly the killer. However, Japanese culture has the same custom. "So the ending doesn't work. It's a cheat."
In an example similar to Encyclopedia Brown, we have the belgian comic character Ludo (not related to that band) who was a detective constantly resolving mysteries and crimes by pointing out that the criminal inevitably was the guy with the black socks. It was always about the black socks, even that one time where he pursued a shoplifter in a bathroom to discover that the guy in question was one of five identical quintuplets. So yeah. Don't wear black socks or else a belgian detective will pin a murder charge on you.
Live Action TV
A rather amusing in-universe example in Star Trek: Deep Space Nine. When O'Brien is marked for death by some crazy aliens because he's one of the last people alive who knows how a forbidden superweapon works, they send a bogus video back to the Federation that shows him dying in an accident. His wife realizes something's fishy because he's drinking coffee in the video and she knows he never drinks coffee in the afternoon, when the video was supposedly taken. But then after the plot is foiled and Miles comes back home, as he's settling in he asks for a cup of coffee. She reacts with astonishment, and he says he drinks coffee in the afternoon all the time!
In an episode of Judge Judy, a man is trying to collect money owed to him by a woman who rented a room from him. He says he provided her with an invoice each month and brought copies showing how much the woman owed him. The invoices had the invoice date on each of them, but they also had a date in the header or footer showing the date they were printed. Judge Judy points out that these invoices are fake because they all have the same date. The guy made the argument that the invoices were created when he said they were, pointing to the invoice dates, but the other date was the current date, the date he printed them. Judy said something like, "I'm not stupid, you know," and ruled in favor of the woman who owed him the money, because apparently to her it's impossible that anyone printing a copy of something would record the date the copy was printed.
Naturally, as a medical mystery, House frequently invokes this trope, much to the frustration of Scott. Once however, it did it on purpose, when House had to deal with an amputee veteran of Vietnam complaining about House's noise. House, noting that the man was a Canadian, and that Canada didn't send troops to fight in Vietnam, attempts to blackmail him with the knowledge. Turns out Canada sent troops to enforce the Paris Peace Accords.
Would you believe CSI: Crime Scene Investigation is accused of this? In perhaps the most memorable chain of cases ever, the identity of the Miniature Killer is revealed by bleach, the only linking thing in the four mini-crime scenes. However, one of them was listed not under the name 'bleach', but by its chemical name, NaCl. NaCl is sodium chloride (table salt) while bleach is sodium hypochlorite (NaClO).
Lampshaded in another episode. Captain Brass decides to reopen an "accidental death" case after he sees the supposedly bereaved husband coming out of a club to hop into a brand new sports car. He later tells the husband that his (Brass') suspicions should've been aroused earlier - when he interviewed the husband, the man said that he "loveD" his wife, and Brass' experience was that innocent people never referred to their loved ones in the past tense so soon after their death. While this obviously (as the accused's lawyer specifically points out) means little legally, it did give Brass more reason to pursue his new suspicions.
And there's an episode where Catherine suspects a mother assisted in a murder her son took part in because something found at the crime scene (I think a body bag) was neatly folded, and Catherine said, "Teenagers never fold things, mothers do!" Apparently clean freak teenagers do not exist in Catherine's mind.
In the Criminal Minds episode "A Higher Power", the case is brought to the attention of the BAU by a cop whose brother had committed suicide recently, which the cop is adamant that his brother would never have done. Making it more suspicious was that the small town the episode was set in had been experiencing a mysterious increase in suicides lately. After getting into the case the BAU discovered that the "suicides" are all being perpetrated by an "Angel of Death" style killer who infiltrates support group meetings, targets members that he feels are suffering too much and would be better off dead, and forcefully arranges their suicides. After catching the killer, the cop thanks the BAU team for believing him about his brother and helping him out... only for the BAU to tell him that they looked into his brothers suicide and found that the MO's didn't match up and the killer had never even made contact with his brother, making his suicide genuine.
A later season episode has a deduction that hinges on this. The killer claims to have witnessed his mother commit suicide by jumping from a bridge where she was sitting on the railing, and from this developed a Nietzsche Wannabe philosophy that leads him to murder people whom he feels are failing to protect their children. However, Reid points out that women rarely commit suicide in that way, and so the BAU accuse the killer, at gunpoint, of pushing his mother off the bridge. This startles him and they're able to take him down without hurting him. But isn't it just as possible that his mother was a statistical outlier?Or that she just slipped and fell accidentally?
In the Leverage episode "The Homecoming Job," Sophie realizes that a Sleazy Politician lied to her about something because he looked her right in the eye when he said it. According to her, the only time any man ever looks a woman in the eye is when he's making a special effort to lie to her.
A bit better then things, because this one was more a snarky line, then a serious deduction.
Web Comics
Used in-story in Tales of the Questor, Quentyn says that some human coins are forged because the heads are facing the wrong way. He's wrong about the heads. The coins, however, really are forged and a guard sees a tradesman's look of utter horror, tipping the guard off to who's behind the forgeries.
