Common misconceptions
Some false beliefs are so widespread they feel like common knowledge. Here's a cheerful correction service for the greatest hits—all verifiable, all things “everybody knows.”
Your body
Myth
The claim: You only use 10% of your brain.
Actually: You use essentially all of it, across the whole day. There is no locked 90%.
Myth
The claim: You swallow 8 spiders a year in your sleep.
Actually: This is a famous fabricated 'fact' — ironically invented to demonstrate how easily fake facts spread. Spiders avoid sleeping humans; the number is made up.
Myth
The claim: Your tongue has separate zones for each taste.
Actually: The 'tongue map' is a misreading of old research. All taste regions detect all basic tastes.
Myth
The claim: Hair and fingernails keep growing after death.
Actually: They don't. The skin dehydrates and retracts, making them appear longer.
Myth
The claim: Shaving makes hair grow back thicker, darker or faster.
Actually: It doesn't change thickness, color or growth rate — studies on this go back to the 1920s. Shorn hair just has a blunt tip instead of a tapered one, which can feel coarser at first.
Myth
The claim: Chewing gum stays in your stomach for seven years if you swallow it.
Actually: Swallowed gum isn't digested, but it doesn't linger either — it passes through your digestive system in a few days, like most other things your body can't break down.
The natural world
Myth
The claim: Bats are blind.
Actually: Bats can see; many see quite well. They also use echolocation. 'Blind as a bat' is just wrong.
Myth
The claim: Bulls are enraged by the color red.
Actually: Bulls are red-green colorblind. They react to the cape's movement, not its color.
Myth
The claim: Lightning never strikes the same place twice.
Actually: It frequently does — tall structures like the Empire State Building are hit many times a year.
Myth
The claim: Dogs age 7 human years per year.
Actually: Aging isn't linear; dogs mature fast early then slow down, and it varies hugely by breed and size.
Myth
The claim: A full moon makes people act strangely (the 'lunar effect').
Actually: Large reviews of crime rates, hospital admissions and psychiatric episodes have found no reliable link to the lunar cycle, despite the belief being common even among police officers and hospital staff.
Myth
The claim: Poinsettias are highly poisonous to children and pets.
Actually: They're mildly irritating at worst — occasional nausea or mouth irritation if eaten, not a medical emergency. The 'deadly poinsettia' idea traces back to a single uncorroborated report from 1919.
Everyday life
Myth
The claim: We only dream in black and white.
Actually: Most people dream in color. The myth may date from the black-and-white-television era.
Myth
The claim: Cracking your knuckles causes arthritis.
Actually: Long-term studies find no link. The pop is just gas bubbles in the joint fluid.
Myth
The claim: Sugar makes children hyperactive.
Actually: Controlled studies don't support it — the effect is largely in the expectations of the observing adults.
Myth
The claim: Microwaves cook food from the inside out.
Actually: Microwaves penetrate only a few centimetres into food and heat that outer layer directly; the centre is then cooked mostly by heat conducting inward — often making the outside finish first, not last.
Myth
The claim: You have to wait 24 hours before reporting someone missing.
Actually: Police and missing-persons organisations are explicit that there is no waiting period — early reporting is actively encouraged, especially for children or anyone in danger.
Myth
The claim: Diamonds are naturally extremely rare, which is why they're expensive.
Actually: Gem-quality diamonds are far more common than their price implies. Prices stayed high for most of the 20th century largely because of tightly managed supply and marketing by major producers, not pure geological scarcity.
Animals get a whole page of their own: animal myths. Food and nutrition too: food myths. And your body and health, in more depth: body & health myths. Misremembering as a group is a special case — see the Mandela effect. And for the newest source of confident nonsense, AI hallucinations.