By foaming, the spitting featherfoot both cools itself and gets rid of unwanted toxins.

The spitting featherfoot, Pennapus saltans, is a strange, strictly herbivorous heteromyid from the North American deserts, from After Man: A Zoology of the Future.

It has small forelimbs and long hind legs, for jumping. The toes are fringed by short, stiff hairs. Its kidneys are highly efficient, recycling the animal's waste water to the point that its urine is more than twice as concentrated as that of a rodent of similar size living in a humid environment.

The featherfoot never drinks water but obtains all the moisture it needs from plants. It can even eat plants that are poisonous to other animals, and has the ability to excrete toxic substances without their having taken part in any metabolic process. It is a nocturnal animal, but if displaced from its deep burrow by a predator during the heat of the day, it can cool itself by producing copious quantities of saliva and coating the front of its body with foam. It also spits at its foe with deadly accuracy. As the saliva contains most of the excreted poisons from the plants it is an efficient weapon. Needless to say this defense mechanism dehydrates the animal very quickly and is therefore used only in dire emergency and even then only for short periods at any one time.

One of the featherfoot's chief predators is the leaping devil.

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