Do you see the one on our left? After every two or three mouthfuls he stops, and takes a look around; he even looks right to the back. Then he takes four or five strides to catch up with the herd, and starts grazing again. Then in a minute or two he takes another look around in the same way. And the sentinel on our right is doing just the same. Yes, the herd is quite safe; the two sentinels are sure to see if any danger comes from their side or from the back. "But will not the sentinels have less to eat, if they are watching half the time?" you may ask. Yes, that is quite true. So all the Papa buffaloes take turns being sentinels. After a while the two sentinels from the ends move up toward the middle, and the next ones then begin to keep watch. And they keep changing places like that from day to day. That makes it quite fair for everybody. When they go to sleep also they are arranged in the form of a crescent; but the two ends are closed up, so that the Papas make a ring, while the Mammas and the children sleep inside the ring. When the Papas lie down, they are closer together than when they are feeding; and they still keep their heads pointed to the outside of the ring, so that they can get up in a minute, and be quite ready to drive off any tiger. Of course they have sentinels keeping watch all the time. But now let us see other wonderful things that the buffaloes do, while they are feeding. We must be very careful how we follow the herd. The ground is now changing, and getting quite rough; so the grass is getting scarce here and there. The buffaloes have not enough grass all the way; so they have to walk on a few yards without eating, till they come to the next patch. Some of the buffaloes are even having a bite at fresh young shrubs in passing, as they will eat anything green, when they have not enough grass. But see! The buffaloes are spreading out, as there are not even enough shrubs in one place. You can see gaps in the line of buffaloes now. And the gaps are getting bigger and bigger! Let us watch a few minutes. Now the gaps are very wide, as some of the buffaloes are lagging behind; and some are turning too much to the side in trying to reach a mouthful from a shrub or a bush here and there. Why, what is happening now? Some of the buffaloes cannot even see one another now, because of the bushes between them! What are the sentinels doing? And what is the leader doing? Suppose a tiger suddenly comes-- But do you _hear_ that? "Moo! Moo!" That is the leader. He has just found out that the herd is spread out too far; so he is calling. He is saying, "Where are you?" "Moo! Moo!" Do you hear that answer? It comes from the sentinel on the right, who is very far away now; but still he has heard the call. His answer means, "Here I am!" And "Here I am!" comes the answer also from the sentinel on the left. "Then close up!" cries the leader.