The waniguchi monster is one of the frequently-copied motifs first known from the famous Shinju-an Hyakki Yakō picture scroll. It is drawn as a transformed waniguchi, a sort of bell or gong hung under the eaves of Buddhist temples and rung by pilgrims upon entering. This instrument takes its name from a split on its bottom which resembles a mouth, which here has fittingly become the jaws of a skulking, fish-like crocodile-creature.

Citations
Yumoto 2005 A p. 31.