Apparently he is very sensitive to nearby vibration or shadow or something. At any rate, he can tell when somebody walks near his crabitat. He used to spend all day hiding in the little hut I bought for him, a half-coconut shell. On the rare occasions that he was caught outside the hut and somebody walked by, he would immediately draw his whole body back into his shell.
Recently, he's become a bit more daring. Not that he's doing tricks or running to the door to greet us or anything, but he's been out of his hut and wandering about the crabitat recently. Sometimes he'll climb around on top of his hut, clinging to the coconut husks with his little claws.
It's kind of neat, being able to see your pet now and then. Maybe the "corral time", the enforced time outside of the little hut, was developmentally helpful to him. Perhaps in the same way that "tummy time" is supposed to be good for babies.
All of that said though, he's still pretty shy. He doesn't always snap back inside his shell when I walk by, but he still sometimes does. More daring or not, I guess sometimes the surprise of somebody getting unexpectedly near is too much for him.
It's most amusing to me when he's walking around on the top of his hut. Like I said, it's a half of a real coconut shell. This means that it's curved. When Lobster suddenly draws his whole body inside his shell, he is no longer able to hold onto the husk. The coconut is also standing right against the plastic wall of the crabitat.
A couple of times today it happened. I got up from my desk to get some water, walking by the crabitat. I saw a flash of movement as Lobster zipped his legs quickly into his shell. All I heard was a CLUNK noise, as he and his shell tumbled off the coconut and wedged into the space between the coconut and the wall.