Why Do Humans Have a 'Third Eyelid'?

Imagine a tiny, flexible curtain that can cover your eye, like a soft shield. That’s your third eyelid, and it helps protect your eyes from dust, bright light, or even tears when you’re crying. It works automatically, so you don’t have to think about it at all.

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Examples

  1. Your third eyelid might come out when you cry a lot.
  2. It covers your eye like a soft curtain if there's dust in the air.
  3. You see it flicker when you're tired and squinting.

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