Why do some animals kill others?

Animals don’t usually kill for sport. If one animal kills another, it is usually for food, or in self-defense. Meat-eating animals, or carnivores, kill vegetable-eating animals, or herbivores, to eat them, as they cannot digest vegetable matter themselves. A natural circle called the food chain is established which enables the different species to survive. Man can eat both meat and vegetables (an omnivore).