The largest bird in the world is also the only bird in the world that has two toes, not three or four. According to the Safari Ostrich Farm in South Africa, most birds have four toes in order to grab their prey. Most flightless birds, like the emu and penguin, have just three toes. The ostrich, meanwhile, has one large toe to carry the weight of its body, which can reach up to 400 pounds, and another for balance. Their unique feet and tall legs allow ostriches to reach speeds of up to 40 miles per hour, according to the American Ostrich Association.
Ostriches also fight with their feet. They can only kick forward, but Science News suggests that their legs are strong enough to disembowel a human being. The birds have been known to kill if feeling threatened.
Dr. Nina Schaller, an expert on the ostrich locomotor system, wrote for the European journal, Science in School, that the majority of the ostrich's "leg musculature [is] located very high on the thigh bone and hip, whereas the lower swinging elements of its leg are comparatively light, moved by long, mass-reducing tendons. This arrangement optimizes the ostrich leg for high-velocity locomotion, giving it both a long step length and a high step frequency."
Schaller also wrote that the ostrich's unique build could inform human prosthetics.