A bull elephant during musth in the Kruger National Park, South Africa. The word actually comes from Hindi and means ‘madness’.
Wikepedia: Musth (alternatively spelled must) is a periodic condition in bull elephants, characterized by highly aggressive behavior, accompanied by a large rise in reproductive hormones – testosterone levels in an elephant in musth can be as much as 60 times greater than in the same elephant at other times. However, whether this hormonal surge is the sole cause of musth, or merely a contributing factor, is unknown; scientific investigation of musth is greatly hindered because, during musth, even the most otherwise placid of elephants may try to kill any and all humans. Often, elephants in musth discharge a thick tar-like secretion called temporin from the temporal ducts on the sides of the head.