The rat learns to open the other problem boxes shown in the photographs in this same hit-and-miss fashion.  In Box II, he has first; to bite the string in two before he can knock up the latch (he never unties the string)!  In Box III, the animal must walk up an inclined plane until the increasing tension on the string causes the latch holding the door in place to rise from its socket.

Myriads of anecdotes are told of dogs and cats opening latches, of dogs buying penny buns and accepting only the correct change in return for a larger coin, of monkeys making up their own beds. The list is innumerable.  These anecdotes were collected by letters, from all parts of the world, taken on trust.

It is perfectly natural for all animals to be hungry and to seek for food even when the obtaining of it offers difficulties.

the evolutionary study of behavior will yield far more fruitful results for the guidance of human conduct than will further studies on morphology alone. And in saying this, we do not mean to decry the usefulness of such structural studies in the past nor their possible value in the future.

It is one thing, however, to watch the habits of birds and foxes, and quite another to experiment with animals as psychologists experiment in their laboratories.