Now that we know why boys play with balls and bats, and girls play with dolls, let us see if we can make out why kittens play with strings and puppies bark after wagons.

Perhaps you have already guessed. The grown up house cat and wild cat get a living all or in part by hunting birds and mice. They crouch close to the ground, creep slowly upon their prey; then seize it with a rush. That is just what the kitten does when you drag some small object slowly across the floor. The kitten doesn’t know why it chases a spool on a string. Really, however, it is playing at hunting small creatures, as its ancestors have hunted them in reality for a million generations.

Puppies are different from kittens. They don’t care much about spools and strings; but they like to run about over the fields and chew up their owner’s shoes. Now the wild dogs, and their cousins the wolves, do not go out alone and hunt small animals as the cats do. They go in packs; and they hunt large animals, wild sheep, wild oxen, deer, which they chase, sometimes, for days at a time. Spools and strings, therefore, are too small potatoes for the puppy; he chases wagons, automobiles and trolley cars, playing he is hunting big game. He doesn’t creep up cautiously on a ball of yarn, not to frighten it. Instead he barks at the top of his voice to call the rest of the pack. He runs away to play with other dogs, because the dogs and wolves are social animals; and when he chews up a rubber boot, he is playing that the pack has killed a moose and he is gnawing the great leg bone.

Of course, the puppy and the kitten do not know that they are playing at hunting when they chase spools and bark at carriages, any more than a boy knows why he likes to climb trees or hit a ball with a bat. But you can see for yourselves that the difference between the play of puppies and the play of kittens is just the difference between the work of a grown cat who hunts small creatures alone, and the work of a grown up dog who hunts large creatures in company.

Not many young creatures, such as we commonly see, do so much playing as puppies and kittens, tho boys and girls do a great deal more. In fact, the wiser any animal is when it grows up, and the more it is able to do then, the more playing it does, and the more interesting games it plays, when it is small. Calves and colts and lambs do not play especially interestingly, because wild cows and horses and sheep do not do much except eat, sleep, and run away from something that threatens to eat them up. But young squirrels, kept in cages, sometimes play at burying nuts in the floor of their cages for their winter supply of food; and young beavers, kept as pets in the house, have been said to play at building dams of chairs, canes, and umbrellas, across the parlor floor. Always, however, no matter how tame the grown animal is, the kitten plays at being a wild cat, and the puppy plays at being a wild dog, and the little boy plays at being a wild Indian; all because cats and dogs and men have been tamed and civilized for only a short while, but ran wild for ages.

There is one game that we all play, children, kittens, puppies, monkeys, and I don’t know how many other young creatures—and that is make-believe fights. We do it with sticks and snow balls and wooden swords; the little animals chase one another back and forth, and pretend to bite and scratch in the fiercest manner, as if they were fighting for their lives. Most animals do have to fight for their lives, many times over; so did most men in earlier times, before we had policemen and jails, and when everybody had to look out for himself.

Did you ever notice that a kitten is ticklish in just the same places that you are? You stroke the kitten’s back or head or legs, and it is as pleased as can be. But you touch it along the front of the body, or around the front of the neck, and at once it begins to bite and scratch and protest its best. All creatures that can be tickled at all are ticklish in the same places; and all these places happen to be precisely the spots where the great blood vessels and other important vital organs are close to the surface, and where, therefore, a wound would be most deadly. So when little animals play at fighting and pretend to bite one another, they bite hard enough to tickle. They don’t like to be tickled any more than you do. So they learn to protect those ticklish places in their play, and when they get to be grown up and fight in earnest, they have already learned not to get bitten in those spots where the bite would do most damage.

So the young animal’s instinct is to play at doing whatever his ancestors have been doing for work; and he has this instinct in order that he may like to do when young what he must do when old; and so have practice in doing it, and learn to do it well. Unfortunately, as men become more and more civilized, they have continually to do more and more new things, while they still persist in liking to do the old ones. That, I suppose, is why some boys and girls do not like to work.