“To gnaw it—that is the right word; hence we give the name of rodents or gnawers to the various animals having incisors of that kind. Such are the squirrel, the hare, the rabbit, the rat, and the mouse, those poor creatures which must gnaw the toughest vegetable substances and fill their bellies with wood, paper, rags even, when there is nothing better for supplying the mill that is kept always going. But it is not merely to satisfy their hunger that these animals are almost incessantly gnawing; there is another reason for their doing it. Their incisors grow all their lives and tend to lengthen indefinitely; consequently, the animal must wear them away by continual friction, as otherwise their crowns would at last so far overlap that they could not be made to meet. Then the poor beast would be unable to seize its food and would perish. In order to be able to eat when hungry, the rat and the rabbit must eat when not hungry, so as to sharpen their incisors and keep them the right length. It is true that they often turn their attention to very poor fodder. A splinter of wood, a straw, a mere nothing suffices to maintain the play of their indefatigable incisors. Remember, children, the expressive term rodents (which means gnawers), applied to a whole class of animals akin to the rabbit and the rat; remember their curious incisors, for we shall have occasion to speak of them again hereafter. For the present let us finish our examination of the rabbit’s teeth. “The canines are lacking; in their place the jaw shows a bar or, in other words, a large open space. At the extreme back of the mouth are the molars, few in number but strong, with flat crowns and several folds of enamel. In fact, they make an excellent grinding machine. “In giving you these details concerning the different shapes of teeth in different species of animals, I wished particularly to point out the following truth: Each species eats a particular kind of food for which the teeth are especially formed, so that one might say of any animal, ‘Show me its teeth and I will tell you what it eats.’ In many instances where we cannot examine the teeth we do not know what such and such a creature feeds on, and in our hasty judgment we mistake a friend for an enemy, a helper for a destroyer. If the animal is ugly we condemn it on the spot and hate it, accusing it of any number of misdeeds. We declare war against it, and never suspect, in our foolishness, that it is a war at our own expense. But there is a very simple precaution by which we can avoid these regrettable mistakes: let us yield to no prejudice, however wide-spread, and before condemning an animal as harmful let us find out what sort of teeth it has. They will tell us the animal’s way of living, as you shall soon see for yourselves.” CHAPTER IV BATS “Which of you three can tell me what bats feed upon?” asked Uncle Paul the next day.