Which bird cannot fly but is the fastest runner?

An ostrich can hold about seventy kilometres an hour in a sprint and keep up fifty for a long way, with a stride that can cover four or five metres. It is the only bird with two toes rather than three or four, and the larger of the two is effectively a hoof - the foot has been reduced to the parts that help it run.

It does not kick backwards like a horse. It kicks forwards, with a claw on that big toe, and there are well-documented cases of ostriches killing lions and people with a single blow. The usual advice about approaching one is not to.

Two more items worth having. Its eye is about five centimetres across, the largest of any land animal, and is physically larger than its brain. And it does not bury its head in the sand - the bird lies flat with its neck along the ground to be less visible, or leans down to turn the eggs in its shallow nest, and at a distance both look like exactly what the phrase describes.