[The crab trying to tuck itself away is kind of a cute image, but Momo manages to restrain himself from pointing that out, particularly when the crab gets together the courage to reply. It sounds a bit...crabby, for want of a better word, and Momo raises his hands in an apologetic sort of gesture, keeping his body language very open. And, pointedly, keeping his hands somewhere obvious enough to reassure that he's not trying to make some kind of sneaky move.]

Sorry, I wasn't sure what to call it. Your shell? [He makes a gesture with his hands as if to surround something, to indicate he was referring to what the crab is living in right now.] We're sorry to be a bother, but we're looking for someone and were wondering if you might've seen them.

[Momo has had to placate far worse things than a grouchy (and, he assumes, possibly just wary of being attacked or something) crab, so he just focuses on honesty for the moment.]