Harry Potter and the Prisoner of Azkaban (Harry Potter, #3)

by J.K. Rowling

Malfoy spent much of their next Potions class doing Dementor imitations across the dungeon; Ron finally cracked, flinging a large, slippery crocodile heart at Malfoy, which hit him in the face and caused Snape to take fifty points from Gryffindor.