Bat spleen is the spleen of a bat. In 1991, on Harry Potters first trip to Diagon Alley he saw a barrel of bat spleens in a shop window. A jar of them was seen on the floor of the First-Floor Girls' Toilets during the troll attack that same year. They are also used in potion-making, and are taught about in sixth year Potions classes. Professor Snape kept a jar of them in his office, and Professor Slughorn briefly mentioned bat spleen as an ingredient in the Draught of Living Death.