"It's true, nevertheless," maintained the doctor, "although I have seen no satisfactory explanation of the changes. They not only make their nests in hollow trees, but in the sides of banks. Were it not for its habit of destroying the eggs and young of birds, the least weasel might be regarded as a wholly useful creature, for it devours innumerable mice, moles, shrews, and insects, and does not attack larger animals or poultry. It is so exceedingly lithe and slender that its prey has no chance to escape. Where a mouse or a mole can go it can go also, and if outrun in the field, it follows the scent of its game like a hound, and is as relentless as fate in its pursuit. They are not very shy, and curiosity speedily overcomes their timidity. Sit down quietly, and they will investigate you with intense interest, and will even approach rather near in order to see better. Dr. Merriam describes one as standing bolt-upright, and eying him, with its head bent at right angles to its slender body. After a brief retreat it made many partial advances toward him, meanwhile constantly sniffing the air in his direction. I've no doubt Dr. Merriam would have liked to know the weasel's opinion. They have two or three litters a year, and the nest is made of dry leaves and herbage. The mother weasel will defend her young at any cost, and never hesitates to sacrifice her life in their behalf. She will fasten herself by her sharp teeth to the nose of a dog, and teach him that weasel-hunting has some drawbacks.