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 profit Abnormal profit persists in the long run in imperfectly competitive markets where firms successfully block the entry of new firms. Abnormal profit is usually generated by an oligopoly or a monopoly; however, firms often try to hide this fact, both from the market and government, in order to reduce the chance of competition, or government intervention in the form of an antitrust investigation. In principle, there are three kinds of abnormal profit: Business writer Michael Porter and Anita M. McGahan undertook an empirical study of the "emergence and sustainability of abnormal profits" in 2003, in which they concluded that both