The spirits that work for Yubaba in the bath house seem to be to varying degrees, froglike. Some seem to be fully frogish, like Aogaeru.

While others are mostly human like Lin, and still others seem to be mixes of human and frog. When Lin is told that she and Sen will be working on the big tub, Lin replies "that's Frog work".

Is there any reason given in Spirited Away or Japanese mythology that explains the frog-like spirits?