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Funny that you would post about this as i learned the same thing the other day in my Bio course! Thought it was so weird cause as a kid I used to think they could just hop out and run around!

I always take pictures of what surprises me :)

That is pretty interesting. I had no idea, since I thought just like @thealeksgreen that they could just leave their shell.

Haha)) By their own they can't leave the shell