LOL, I bought some live rock one time and one of those critters hitch hiked on it to my salt water aquarium, I always noticed that some of my fish kept disapearing and sometimes I would hear this loud "click" noise coming from the aquarium, good thing he never clamped his claw in front of the glass, that would have been bad.
Anyways, I spotted the little bastard hiding in one of the rocks one day, I didn't want to mess with him as he could really fuck up a hand if he got a hold of you, so I left him in there