Some birds use the beak to dig in the ground, as the bank swallows, while the barn swallows make it a trowel, to carry and plaster mud (Fig. 3). All of them use it as a hand to feed themselves, and a brush and comb to dress their feathers. [Illustration: FIG. 3. Bill of Swallow.] Birds need to use the beak a good deal, because in most cases it grows like our finger-nails. If they did not keep it worn off, it would grow so long as to trouble them. Sometimes when a bird lives in a cage and does not use his bill, it grows so long that he can hardly pick up his food. The woodcock's long beak is sensitive, so that he can feel the worms, deep in the mud where they live. Many waders and swimmers have beaks soft like leather. [Illustration: FIG. 4. Bill of Hawk.] You can tell by the shape of the beak how a bird lives, and what he eats. The strong, hooked beak of a hawk shows that he catches live animals to eat (Fig. 4). The long, narrow, sharp bill of a heron shows that he spears his prey, often under water. The sharp-pointed bill of a warbler is to pick tiny insects and eggs out of blossoms, and from under leaves. The sharp-edged bill of a sparrow (Fig. 5) is to break open the hard shells of seeds. [Illustration: FIG. 5. Bill of Sparrow.] The curious beak of a crossbill (Fig. 6) is to pick seeds out of pine cones. [Illustration: FIG. 6. Bill of Crossbill.] A duck's wide beak, with a strainer at the edge, is to let water out while keeping food in. A spoon-shaped bill is to scoop up food, and a thin, flat one is to poke into narrow cracks. Both parts of the beak, which take the place of our jaws, are called mandibles, upper and lower. Both of them can be moved, while we can move only our lower jaw. Birds' tongues are as curious as their beaks. To all birds they take the place of a finger, as the beak takes the place of a hand, and they differ as much as the beaks from each other. Insect eggs are very small, and often packed snugly into cracks and corners, and the birds who eat them have a brush on the tip of the tongue, which brushes an egg out of its hiding-place very easily. The nuthatch picks his small grubs out of crevices in bark with the four-tined fork at the end of his tongue. A hummingbird's tongue can be used as a tube, to draw up the honey of flowers, or perhaps as a pair of tweezers, to pick out the tiny spiders that live there. A woodpecker has barbs on his tongue, to spear insects hidden under the bark, as shown by Mr. Lucas (Fig. 7). It is said to be sticky also, to hold small ones, like ants. The tongues of birds are of many shapes, but each one is fitted to its owner's way of getting a living. [Illustration: FIG. 7. Tip of Tongue of Downy Woodpecker.] Because the tongue is often horny, and they eat strange things, it is sometimes thought that birds have little sense of taste. But we cannot be sure of this, and we know they all have notions about their food.