Ferocious Fighters (S04E06)

The Siamese Fighting Fish displays such ferocity that it battles its own reflection to the point of fatigue. New studies reveal that this combative behavior is influenced by the individual temperament of each fish. In a surprising twist, male kangaroos have historically been matched against humans in boxing matches. The strongest male kangaroos are muscular powerhouses, equipped with lethal kicks. What drives these creatures to fight, and what attributes are essential for emerging victorious?