Bird feet are usually built around four toes, and the flightless ratites mostly kept three. The ostrich went further. Each foot carries only two forward toes: a very large third digit tipped with a broad nail, and a smaller fourth digit that has no nail at all and often lifts clear of the ground at speed.
The arrangement concentrates weight on a narrow contact patch, much as the single hoof of a horse does. Ostriches are credited with sustained running around 55 to 70 kilometres per hour over open ground, and stride lengths in the region of three to five metres have been recorded. The reduced foot also stores and returns elastic energy through long tendons in the lower leg.
What is often overstated is the kick. Ostriches can and do injure people, and the large toe nail is a real weapon, but claims that they routinely disembowel lions circulate far more widely than any documented case.