Self preservation, ironically. They normally spend all day swimming around leisurely, but can do a tail flop to escape danger quickly. I say ironically (don't

Self preservation, ironically. They normally spend all day swimming around leisurely, but can do a tail flop to escape danger quickly. I say ironically (don't kill me if I'm misusing the word) because that same big abdominal muscle leads to creatures, especially humans, seeking them out for their meatiness. See: https://en.m.wikipedia.org/wiki/Caridoid_escape_reaction https://en.m.wikipedia.org/wiki/Caridoid_escape_reaction