Notice all the little red crabs in the picture below? As you walk along the beach you can see them up ahead scrambling to find their hole in the sand as you approach.
They are fairly small, only about 2 to 4 inches, claw to claw. As you get close they sit halfway in the hole until it seems you are getting too close, then they will disappear into the hole.
After the tide recedes, they will remove the sand from their hole and distribute it in a pattern of little beads. We have no idea how this is done but sometimes the patterns are quite interesting.
What can I say? We have time on our hands that allow us to ponder such things.