Refrigerator skull

From Walkypedia!

The refrigerator skull was discovered by Joyce [1] in the apartment she shared with Walky after their SEMME days had ended. She asked Walky why it was there, but he seemed unperturbed by its presence and explained that he had put it there to keep it from spoiling.

Later, Billie found a skull in her refrigerator. [2] Walky took it away, saying, "Oh, hey, I've been looking all over for you." Danny audibly commented that Walky has their spare housekey, so it seems likely that this is the same skull, and that Walky accidentally left it at the Wilcox's house during a previous visit.

The identity of the skull's former owner is currently unknown.