A Boggart is a shape-shifter that takes on the form of its intended victim's worst fear. It generally likes to hide in dark, enclosed places, such as in cupboards, under beds, or in hollow trees. Since a boggart changes shape upon sight, few know what one actually looks like in unaltered form. In Harry Potter and the Prisoner of Azkaban, Professor Lupin teaches his students in Defence Against the Dark Arts to approach a boggart. A common wizards' defence against a boggart is to use a spell to make it appear amusing, since boggarts are weakened by laughter. This is achieved by pointing a wand at the boggart and saying "Riddikulus" while thinking of something very funny in order to turn the boggart into something funny.