A parody of the japanese fairy tale, in which a monkey threw some hard, unripe persimmon at the mother crab who were asking for some persimmons for her child.. The crab child later got offer by others (i kinda forgot, it's stone mortar, and 2 others) for revenge..
Definitely a reference to the Crab and the Monkey story. That monkey pelting Oboro (known for crabs) is what is making Ushio go "Now where have I seen this...?"
