The Experimental Cow Ending is an Ending in Prisoners of the Elder One. It occurs after entering the main room of the Elder One's Hideout after having eaten either the cookies in the Doll Room or the feast on the dining table in the Dining Room.
Ixies put a spell on all the food in the mansion, which swells Erik's chest out into a large pair of milky teats. Completely debilitated by their new bust, Erik spends the rest of their life as a dairy cow/test subject for Ixies.