Fred and George Weasley were planning to release some in Hogwarts School of Witchcraft and Wizardry in 1996, during Dolores Umbridge's tyrannical tenure as Headmistress, but they left the school before they had a chance. Their sister, Ginny, merely had to mention it to prevent students from traversing down a school corridor, which allowed Harry Potter and Hermione Granger to break into Umbridge's office to use her fireplace for communication.