Boar Shit is an ingredient used to make a sandwich, which is given to Mr. Boar.
Rusty Lake Hotel[]
In Mr. Boar's room, he demands the player make him a sandwich. His feces is taken from the toilet and used in the sandwich, which he promptly eats. The tainted sandwich upsets his stomach and causes him to go to the bathroom, where he leaves more feces in the toilet which can be taken and used in another sandwich.