Knockturn Alley is a dingy alleyway where the shops are devoted to Dark Arts items. The alley is connected to Diagon Alley near Gringotts. There are stores selling shrunken heads, live gigantic black spiders, and poisonous candles. Street vendors include an old witch with a tray full of whole human fingernails. And somewhere in the alley, according to Hagrid, someone sells Flesh-Eating Slug Repellent.