If it can cut through something this small, imagine what it can do to the rest of you!
One way of showing the sharpness of a blade is dropping a strand of hair, or thread, on it and watch it split it in half. Other items used to demonstrate the blades sharpness include silk fabric or a cushion. An absurdly sharp blade will likely make a sound, too.
Not to be confused with splitting hairs, which is about fine distinctions.
Examples:
open/close all folders
Comic Books
- Often subverted in Superman stories, especially in the height of the Silver Age, when Superman appeared to get amnesia about every other issue. They proved to him who he was frequently by trying to cut his hair with scissors - and the scissors would be cut by the hair, instead.
Fan Works
- Various Vytal Ventures, "Hard and Soft": Ren does this to test his Storm Flower after cleaning and sharpening them.
Films — Animation
- In The Adventures of Ichabod and Mr. Toad, Brom Bones intimidates Ichabod during his telling of the legend of the Headless Horseman by slowly splitting a hair off his head with a large knife.
Films — Live-Action
- The Bodyguard: Frank Farmer demonstates the sharpness of a katana he owns by taking a silk scarf off the woman he's bodyguarding and letting it float down onto the blade, where it's cut by just its own weight.
Gamebooks
- In Tunnels Of Fear, a monster gleefully demonstrates the sharpness of its broadsword by swinging it at a huge cobweb, which is sliced cleanly, without a single thread pulling away from the wall.
Literature
- On Gor, blades are frequently described as being "so sharp it would cut a piece of silk dropped on it."
- In Sir Walter Scott's The Talisman, Saladin demonstrates the sharpness of his Saracen sword by dropping a cushion onto it, which is neatly sliced in half.
- Shows up in Frank Stockton's short story The Discourager of Hesitancy
(a sequel to his more famous "The Lady or the Tiger?").
- The split-a-piece-of-silk variant appears in Interesting Times, when a samurai attempts to intimidate Cohen the Barbarian by cutting a silk handkerchief this way. Cohen then subverts it by throwing up a bogey-covered hankie, and decapitating three of them as they look up before they realize what's happening.
- In The Hardy Boys mystery "The Secret of Pirates' Hill", Joe drops an envelope on the blade of some pirate cutlasses in the museum to test it's sharpness. {Hint, it's very sharp}
- In Water Margin, Yang Zhi, one of the novel's heroes, is forced to sell his family heirloom of a sword in the street. When confronted by a drunken local bully who demnds a dirt cheap price, he tells the latter that the sword is capable of "cut metals like mud, slice through hair by the merest touch, and kill people with no blood on the blade". It's all true, and Yang Zhi proved the third feature on the bully himself.
- In Protector of the Small, Raoul demonstrates the sharpness of Kel's naginata to Flynn by placing a feather on the blade. It, of course, cuts the feather in half without any effort. Kel also tests the sharpness of a blade sent by her Anonymous Benefactor with a hair from her head.
- Noticeably averted in Inheritance Cycle where while training a dragon rider to care for his weapons properly an actual metalsmith points out that you don't want that sharp an edge on most blades, being that fine of a point also weakens the metal by making it so thin it can cut hair meaning the sword in question wouldn't last very long before being damaged beyond the point of usability as a sword rather then a mace.
- Thidreks Saga: For the smithing contest against the king's smith, Weland the Smith forges a sword and tests it by throwing a felt hat into a stream and letting it drift down on the sword's edge, so that the hat is cut in two. Despite the apparent success, Weland breaks the sword and forges the fragments into a new blade, then repeats the test with a blanket, which also is cut in half. Nevertheless Weland repeats the process another time; only when the third sword passes the test against an even thicker blanket, he is satisfied. Notably the author seems not to have understood the logic of the trope, as the objects tested against the sword's edge get heavier each time; since it is implied that Weland is raising the bar with each test, the objects used should get lighter.
Mythology
- Honda Tadakatsu, a samurai from 16th Century Japan, carried a spear named Tonbokiri, or Dragonfly Cutter, because it was said to be so sharp that a dragonfly landing on the tip would be sliced in half by its own weight.
Theatre
- In Sweeney Todd: The Demon Barber of Fleet Street, during the contest with Pirelli, Sweeney does this. Generally, on-stage, he pulls one of his hairs out, slices it, and watches it fall to the ground, all during a pause in Pirelli's song.
Video Games
- Samurai Warriors: In Honda Tadakatsu's route in the first game, his opening cinematic shows a dragonfly land on the blade of his spear only to be split in half by its own weight. This was a reference to the legend that the real Honda Tadakatsu's spear was that sharp.
Webcomics
- Gunnerkrigg Court: Kat and Annie test the Coyote Tooth, a blade made from the fang of a Physical God, by dropping a steel ball bearing on the edge; it's bisected without even slowing down.
Western Animation
- Looney Tunes
- Ali Baba Bunny: Hassan manages to chop Daffy Duck's hat, the diamond on it, and finally, the hair on his head.
- In Broom-Stick Bunny, as Witch Hazel is about to prepare Bugs for a brew, she remarks that her cleaver is "sharp enough to split a hair. Split a hare? AHAHAHAHAHAHAHA!"
- Subverted in the short A Bear for Punishment, when Junyer tests the razor, the hair splits just fine, but as Junyer Does Not Know His Own Strength he wrecks the blade as the follow-through of the swing smashes it on a table.
- Played straight and inverted in a Popeye short where Popeye and Bluto were competing store salesmen. Bluto shows that his knives are quality with this trope, then Popeye shows how crappy they are by having the hair split the knife.
- A similar gag happened in the Talkartoons short "Dizzy Dishes".
- Johnny Bravo has a similar joke when Johnny enters a lumber-cutting competition. After a lumberjack splits a hair with his axe, Johnny splits an axe with his hair—which was still on his head.
Johnny: My hair is ready.
