No matter where you live, the grass usually looks greener elsewhere. Even crabgrass. Consider the hermit crab, who must dwell in a shell and is forever on the lookout for a better one. Every time he finds the ideal, empty seashell to protect his soft, unarmored abdomen, he grows some more and starts house hunting again. He tries on new homes like we try on new clothes and, like us, discards them when he puts on a little weight. But crab rehab is easy - all he needs is a sunken living room.