The answer is, of course, in the movements of the fish’s tail. The fish in swimming is surrounded with water, top, bottom and all sides of him. The pressure of the water on the fish is the same at all points so that any motion made by him would have a tendency to make him move. As a matter of fact the tail in moving from side to side creates a current in the water from the head to the tail, or rather would produce an actual current if the fish remained perfectly still. Instead of making an actual current of water, the body of the fish is moved forward. As to whether the water ahead of him opens up first and then the water behind him is a more difficult question to answer. To the appearance it would seem as if the water moved at both ends and sides at once, but according to scientific theory, the water at the head of the fish is displaced first. Why Are Birds’ Eggs of Different Colors? This is a wise provision of nature to help the mother birds hide her eggs away from the eyes of her enemies. In the animal kingdom every kind of life is the natural prey of some other kind of animal. A bird will have enemies which try to catch her as food. A bird cannot fight back, so must fly away when danger threatens, in order to save her life. This means that she must leave the eggs in the nest for the time being. At certain times she must also leave her nest and search for food for herself. In order that the eggs so left alone may have a better chance of not being discovered, nature has arranged matters so that the eggs take the color very much of the surroundings in which they are laid. Eggs of some birds are spotted or look like pebbles, because the mother bird lays them in the sand. Some of them are green, almost the color of the materials from which the bird builds the nest, and so the colors have a real, and to the birds, a valuable purpose. Why Does a Hen Cackle After Laying an Egg? The hen cackles because she is glad. She is glad because she has just accomplished something, which she was put on earth to do. If you study the life on the earth carefully with this in mind, you will discover that all kinds of life give expression in some form of gladness, when they have performed the things they are on earth for. It’s the hen’s way of expressing herself and letting the chicken world know. The dog wags his tail when he is pleased; boys and girls jump up and down when they are pleased, whether they have been doing anything commendable or not. No doubt also the actual laying of the egg causes some discomfort to the hen and the corresponding feeling of gladness would come naturally after the discomfort disappeared. Why Will Water Run Off a Duck’s Back?