When you're startled, you experience a sudden jolt of surprise that makes your body react before your mind catches up. You might jump, gasp, or freeze when someone sneaks up behind you and says “Boo!” or when a book falls off a shelf with a loud crash.

Being startled is a physical feeling as much as an emotional one. Your heart might race, your muscles might tense up, and you might feel a quick rush of energy through your body. It happens in an instant, triggered by something unexpected: a loud noise, a sudden movement, or someone appearing where you didn't expect them.

A startling discovery is one that catches you off guard, like learning that octopuses have three hearts or that your quiet classmate is a champion chess player.

After being startled, you usually calm down quickly once you realize there's no real danger. That moment of being startled, though brief, reminds us how alert our bodies are to unexpected things happening around us.