Some people cringe at the thought of getting tickled. Some scream and run away. But no matter how miserable it can be for some people, being tickled often triggers the same reaction: laughter.
But why?
It's a question that has puzzled some of the world's most famous minds for over 2,000 years. Scientists still don't have all the answers. But they do know that humans aren't the only animals that laugh when they're tickled. Apes and rats do, too.
Most human laughter is brought on by seeing or hearing something funny. But laughter from tickling is an automatic physical reaction. And that, some scientists say, is just plain weird.
There are two main types of tickles. One is a light touch, like a bug crawling across the skin. That kind doesn't make people laugh. The other kind of tickle uses more pressure. It's usually aimed at a tender part of the body such as the feet, armpits, or throat. This type of tickling activates the part of the brain that controls our voice and feelings. It causes laughter.
It also triggers the part of the brain that controls the human body's natural defense system. Some scientists think it's possible that tickle laughter came about as a way for humans to protect themselves. Laughter is a sign of surrender that tells an attacker, "I'm not a threat."
Other scientists think tickling might have evolved as a way to encourage playfulness. For social animals, play is an important part of learning.
Studies have shown that apes laugh a lot like humans when they're tickled. One study showed that even rats have their own version of tickle giggles. They let out high-pitched squeaks that human ears aren't able to hear. The rats in the study even chased after the tickling hand. They kept laughing as they ran!
Scientists still don't fully understand what causes humans and other animals to chuckle when they're tickled. But they do have a clear answer to one question: Why can't people tickle themselves?
Here's the reason: One part of our brains knows the sensation is about to happen, so the part of our brains that controls laughter isn't triggered.
QUESTION 3
3 / 4
Which passage from the article best supports the idea that tickle laughter can be a defense system?
Some scientists think it's possible that tickle laughter came about as a way for humans to protect themselves.
There are two main types of tickles. One is a light touch, like a bug crawling across the skin. That kind doesn't make people laugh.
Most human laughter is brought on by seeing or hearing something funny. But laughter from tickling is an automatic physical reaction.
Scientists still don't fully understand what causes humans and other animals to chuckle when they're tickled.