“All nocturnal birds of prey practise this undignified method of freeing the stomach: they throw up in a ball the rejected remnants of what they have swallowed whole. If you ever find yourself near an owl’s retreat, examine the ground beneath it: the balls of little bones and hair will tell you from how many mice and other rodents of all kinds these birds deliver us.” “I have seen some of those balls near a rock all white with bird-dung,” said Louis. “Some owl certainly lived there. It was responsible for the dung and the balls of refuse that you saw.” CHAPTER XIII RATS “Let us return for a moment to the rodents, the habitual prey of the night-birds. You do not know them all, by any means, but we ought not to pass them by; for if some, like the hare and the rabbit, are useful to us, still more are very destructive. You remember those two pairs of incisors, so long and sharp, that I told you about when I described the rabbit’s teeth. All rodents have similar incisors. To keep them sharp and prevent them from overlapping too much by growing too long, which would make it impossible for the animal to feed itself, the rodent must wear them down by constant friction as fast as they grow. Consequently, these terrible incisors have, so to speak, no rest; they must always be nibbling something, no matter what. Thus the harm they do us is much greater than you would suspect from the size of the animal. How much actual food does a mouse need for one meal? Very little, unquestionably. A mouse is so small that a single nut will fill its stomach. Don’t think, however, that one day’s ravages are confined to that one nut. After the nut is eaten, the animal will proceed, perhaps, to gnaw a hole in a bag, reduce a piece of cloth to tatters, chew up a book, or drill a hole in a board, simply and solely to whet its teeth. And the damage caused by rats and mice in our dwelling-houses is matched by other damage caused by other rodents in the fields. You must make the acquaintance of all these destroyers.” “For my part,” Jules confessed, “I shouldn’t, if I saw it, know the field-mouse that you told us about in your talk on night-birds.” “I know rats and mice such as we have in the house,” said Emile, “but that’s all.” “And yet,” rejoined his uncle, “I very much doubt whether you have any real knowledge of the rat. I will begin with it.