Tommy didn’t say anything, but he thought of the playmate who forgot and swam out beyond the bulrushes, and, when he had hunted and hunted and couldn’t find him, he knew that Hooty had not visited the Smiling Pool for nothing. So Tommy learned the great lesson of never being careless and forgetting. Later that same night, as he sat on a little muddy platform on the edge of the water eating a delicious tender young lily-root, there came that same warning slap of a tail on the water. Tommy didn’t wait for even one more nibble, but plunged into the deepest water and hid as before. This time when the signal that all was well was given he learned that some one with sharper ears than his had heard the footsteps of a fox on the shore and had given the warning just in the nick of time. Four things Tommy learned that night. First, that, safe and beautiful as it seems, the Smiling Pool is not free from dangers for little muskrats; second, that forgetfulness means a short life; third, that to dive at the instant a danger-signal is sounded and inquire later what the danger was is the only sure way of being safe; and fourth, that it is the duty of every muskrat who detects danger to warn every other muskrat. Though he didn’t realize it then, this last was the most important lesson of all. It was the great lesson that human beings have been so long learning, and which many have not learned yet, that, just in proportion as each one looks out for the welfare of his neighbors, he is himself better off. Instead of having just one pair of little eyes and one pair of keen little ears to guard him against danger Tommy had many pairs of little eyes and little ears keeping guard all the time, some of them better than his own. Eating, sleeping, and playing, and of course watching out for danger, were all that Tommy had to think about through the long lazy summer, and he grew and grew and grew until he was as big as the biggest muskrats in the Smiling Pool, and could come and go as he pleased. There was less to fear now from Hooty the Owl, for Hooty prefers tender young muskrats. He had learned all about the ways of Reddy Fox, and feared him not at all. He had learned where the best lily-roots grow, and how to find and open mussels, those clams which live in fresh water. He had a favorite old log, half in the water, to which he brought these to open them and eat them, and more than one fight did he have before his neighbors learned to respect this as his. He had explored all the shore of the Smiling Pool and knew every hole in the banks. He had even been some distance up the Laughing Brook. Life was very joyous.