Title. Skull is made of bone too. Grinder grinds bones into bonemeal, so why not skulls aswell?
because skull put into the press gives you blood and bone. put the bone in the grinder and there you have your bonemeal from skulls. blood is needed for advanced compost and growing lotus flowers(used for potions).you can also put any head(animal/ human skull) into the press and get blood and bone