Cassowary

Some Australian flora couldn't grow without this vibrant, flightless bird. Some seeds, which are too big for other frugivores to consume, can only sprout after passing through the cassowary's digestive system. So that's one advantage it has.

The most lethal bird in the world is the cassowary, though. It has a 4-inch claw on each foot that resembles a dagger and is able to "chop open any possible threat with a single fast kick." Its scary resemblance to velociraptors is increased by its running speed of up to 50 km/h and its roughly seven-foot vertical jump. They even scare one another. Cassowaries are typically loners and only occasionally show affection to each other. Men are prone to intimidate one another, whereas women can make men run away with just a glance. But when they do speak, it's through extremely low frequency booms, whose rumble we can actually feel in our bones.

It's not unexpected that the cassowary has occasionally killed people. Typically, they jump, kick, charge, or headbutt their prey, leaving "puncture wounds, lacerations, and bone fractures." Cassowaries are known to kick and peck at doors and windows, occasionally shattering glass, thus staying inside is useless. Interestingly, though, it's believed that this is an attack on their reflection before it even happens. It seems that cassowaries are so terrifying that they are afraid of themselves.

Kingdom: Animalia
Phylum: Chordata
Class: Aves
Infraclass: Palaeognathae
Order: Casuariiformes
Family: Casuariidae
Genus: Casuarius