Fear of mice avoid a mouse, showing there may be some basis for this belief. It is not known why elephants should react in this way, though there are several theories. Regardless, elephantine murophobia remains the basis of various jokes and metaphors. The classical board game Dou Shou Qi has the Rat kill an Elephant: as multiple editions of the rule book mentions that the Rat would crawl into the Elephant's ears to gnaw into its brain: but this is considered to be a folk tale. Gertrude of Nivelles is the patron saint of murophobia, and is also invoked against rats and mice
Abnormal behaviour of birds in captivity other birds, however, after being sold and taken to the owner's home, birds in captivity are often housed in isolation and in environments lacking abundant resources or complex stimuli. In the United States, it is estimated that forty million birds are kept caged and improperly cared for. Because of these inappropriate housing conditions, abnormal behaviour patterns may appear in caged birds kept as pets. Once established, these abnormal behaviours in birds are often not alterable. When social interactions amongst birds are absent or inadequate, abnormal social behaviour may develop. For example, a study regarding parrots that had been isolated in