Hermione pulled her knees up to her chest and wrapped her arms around them, gnawed on her lip thoughtfully, a grin spreading stupidly over her face. "Psychology is the Muggle study of the human mind and brain. Reverse psychology is... basically, pushing someone to do what you don’t want them to do, with the expectation that either the push itself, or the way you do it, will make them do the opposite. What you really want them to do."