Here's an Illusion That Makes the Brain Think it's in Danger When it's Not

It is possible to trick the mind into thinking that a completely fake hand is actually your own. By keeping your hand out of sight and only letting the fake hand appear in the line of sight, your brain will concentrate on just the fake hand.

Moreover, by using a brush to simultaneously stroke your real hand and the fake hand while your real hand is out of sight, your mind will start to synchronize what it feels with what it sees.

So when someone comes up and stabs the fake hand with a fork, you can understand why the mind believes that your hand is actually in danger.

This is actually an evolutionary trait of the brain. It's wired to protect itself, and illusions such as this demonstrate how the brain works to get out of the way when it senses danger.