A cockroach is an insect and a potion ingredient. When Severus Snape was Potions master at Hogwarts School of Witchcraft and Wizardry, he kept a jar of these insects (deceased) in his office. In 1996, after Snape caught Harry Potter looking at his private memories through the Pensieve, he kicked Harry out of his office and threw the jar of cockroaches, which smashed just over Harry's head. In 1993, during the Defence Against the Dark Arts class that covered boggarts, the boggart turned into a cockroach just before taking the form of Severus Snape when Neville Longbottom stepped in to finish it off. Cockroaches may be an ingredient in Cockroach Clusters.