People have often marveled at how an elephant, so large and heavy, can walk calmly through swamps where other animals would struggle.
It turns out that this is due to the unique structure of its legs. An elephant’s foot is essentially encased in a leathery pouch. The bottom of this pouch is firmly attached to the bones of the foot, while the walls rest freely on the muscles. When the elephant steps down, it bears its full weight on the leg, causing it to swell and expand. Then, as it lifts its foot to take a step, the leg compresses.
This is why elephants are not at risk of sinking into the mire. As soon as they lift their foot, it becomes slimmer and easily pulls free from the mud.