Reflexes
Reflexes is how your body moves on its own to keep you safe, like pulling your hand off a hot stove.
Think of it this way
A spring-loaded lid sits on a pot on the stove. Press it down, and it snaps right back up on its own. You do not decide to let go — it just fires. Your reflexes work the same way: a signal hits a nerve, and your body pulls back before your brain weighs in.
Explaining reflexes by grade level
When someone drops a ruler and you catch it, your hand moves fast. You did not plan to grab it. Your body acted on its own. Some people catch the ruler sooner because their bodies send signals at different speeds.