It takes seven years to digest gum
While it may prove a bit more difficult to break down than organic foodstuffs, chewing gum gets no special treatment from the digestive system. Doctors figure this old wives' tale was invented to prevent kids from swallowing the rubbery substance.
The Great Wall of China is the only manmade structure visible from space
There are several variations on this folkloric statement, and they're all quantifiably false. Astronauts can spot the Great Wall from low-Earth orbit, along with plenty of other things like the Giza pyramids and even airport runways. But they can't see the Wall from the Moon.
Humans use only 10 percent of their brains
This media darling has been around for at least a century. Fortunately, it's just not true. MRI imaging clearly demonstrates—with fancy colors no less—that humans put most of their cerebral cortex to good use, even while dozing.
Adults don't grow new brain cells
Much of a human's crucial brain development happens during childhood, but it isn't all downhill from there. Studies have shown that neurons continue to grow and change well into the adult years.
Water drains backwards in the Southern Hemisphere due to the Earth's rotation
Not only is the Earth's rotation too weak to affect the direction of water flowing in a drain, tests you can easily perform in a few washrooms will show that water whirlpools both ways depending on the sink's structure, not the hemisphere.
Animals can predict natural disasters
There is no evidence that animals possess a mysterious sixth-sense allowing them to predict natural disasters. Their keen senses of smell, hearing, and sharp instincts alone are enough to send them scattering for the hillsides during a hurricane or tsunami. And even so, animals often die during natural disasters, so if they do have some sort of sixth sense, it's not worth much.
A penny dropped from the top of a tall building could kill a pedestrian
A penny isn't the most aerodynamic of weapons. A combination of its shape and wind friction means that, tossed even from the 1,250-foot Empire State Building, it would travel fast enough merely to sting an unlucky pedestrian.
A dog's mouth is cleaner than a human's
Despite a habit of licking things no human would dare, Fido's mouth is often touted as scientifically more sterile. Truth is, oral bacteria are so species-specific that one can't be considered cleaner than the other, just different.
Men think about sex every seven seconds
Males are driven to reproduce, evolutionarily speaking, but there is no scientific way of measuring to what extent that desire consumes their everyday lives. Thankfully, for world productivity as a whole, seven seconds seems a gross overstatement, as best researchers can tell.
Lightning never strikes the same place twice
In fact lightning favors certain spots, particularly high locations. The Empire State Building is struck about 25 times every year. Ben Franklin grasped the concept long ago and mounted a metal rod atop the roof of his home, then ran a wire to the ground, thereby inventing the lightning rod.
A falling cat will always land on its feet
Studies have demonstrated that, when dropped from most heights, cats will land gracefully on their feet. Results change only with cats dropped upside-down from a height of one foot or less. We're not suggesting you try this at home.
Yawning is "contagious"
Empirically, this is tough to deny; perhaps you'll yawn while reading this. The real question is whether there's actually something physiological at work here, and the answer is likely yes: even chimpanzees mimic each other's yawns.
Eating a poppy seed bagel mimics opium use
Purveyors of this urban legend call on a popular Seinfeld episode for support. It turns out there's truth behind the comedy: tests suggest ingesting just two poppy seed bagels may produce a positive result for opiates on a drug screen.
There is no gravity in space
Blame the term "zero-gravity" for this common misconception. Gravity is everywhere, even in space. Astronauts look weightless because they are in continuous freefall towards the Earth, staying aloft because of their horizontal motion. The effect of gravity diminishes with distance, but it never truly goes away. Oh, and while we're at it, it's also untrue that space is a vacuum. There are all kinds of atoms out there, albeit sometimes far apart (and this thin gas adds to the collective gravity budget, too!)
Chicken soup can cure the common cold
Cure is a strong word, but science suggests Moms around the world are still right in forcing spoonfuls of chicken soup down their kids' throats. Studies have found that the broth actually contains anti-inflammatory properties that help reduce congestion.
Seasons are caused by the Earth's proximity to the sun
The Earth's distance from the sun during its yearly elliptical orbit actually has little effect on temperature. It's the angle of the Earth's tilt—toward the sun in the summer for the Northern Hemisphere and away in the winter—that dictates climate.
Chickens can live without a head
True, and not just for a few minutes. A chicken can stagger around without its noggin because the brain stem, often left partially intact after a beheading, controls most of its reflexes. One robust fellow lived a full eighteen months. Likely he was a real birdbrain, however.
Hair and fingernails continue growing after death
Though hair and fingernails appear to keep growing after death, this is merely a morbid optical illusion at work. In death the human body dehydrates severely, retracting enough skin to expose more nail and hair.