Ghost Crabs on the flats. The one-eyed crab was one bad dude - wasn't scared of me at all (or maybe he couldn't see me...).
The other crab was demonstrating a tactic they all seem to use - run to the water and bury yourself if confronted with something bigger than you are.
I saw one other situation today that explains the tactic - a moray got hold of a crab and was plucking legs off one at a time. If you can bury yourself, the moray can't get you (moray are good at getting in crevices, but they can't dig).