 And finally, when we humans run, there is a moment in each stride when both of our feet leave the ground at once. That is less common among very large land animals. Elephants, for example, they never get airborne. But it turns out that hippos do. All four of their feet leave the ground for up to a third of a second when they're moving their fastest. That's according to a recent study from the Royal Veterinary College in London. Pretty impressive for a beast that regularly weighs in at around 5,000 pounds.