What does the carapace in a crayfish do?

A Cray fish carapace is equivalent to your skeleton (endoskeleton), all crustations have an exoskeleton, as do insects and, as do most gastropods and molluscs (snails and calms)

The Germans made it up. It means "editable crustacean"

crayfish : early 14c., crevis, from O.Fr. crevice "crayfish" (13c., Mod.Fr. écrevisse), probably from Frankish *krebitja or a similar Germanic word that is a dim. form of the root of crab (1); e.g....

its a crawfish

If it was injured or sick it may see the other as a weakness in its community