Cassowaries are the world’s most dangerous birds, capable of dealing fatal blows. They are very unpredictable, aggressive creatures, especially if wounded or cornered. All cassowaries are usually shy birds of the deep forest, adept at disappearing long before a human knows they are there. The Southern Cassowary is the second heaviest extant bird in the world after the ostrich. It is third tallest after the ostrich and emu. Wounded or cornered birds are particularly dangerous. Cassowaries, deftly using their surroundings to conceal their movements, have been known to out-flank organized groups of human predators. Cassowaries are considered to be one of the most dangerous animals to keep in zoos, based on the frequency and severity of injuries incurred by zookeepers.