Why do you see squiggles when your eyes are closed?

Question

Those squiggly things that look like worms and seem to move around. What are they?

Answer 1

do you also see them when you look at the bright sky or a blank wall?  if you do, they are floaters..they are little pieces of vitreous material  

Answer 2

I dunno but it's really cool. And freaky. =P