Bruce Cline, age 10, of Montgomery, Ala., for his question:

How can birds eat seeds without teeth?

It is winter, and the pretty finches are down in Alabama, searching the meadows for weed seeds and gritty grains of corn. They have no teeth to chew this hard food, but each little bird has a special stomach called a gizzard. The gizzard is a leathery muscle which works like a strong, clenched fist. It pounds and squeezes even the hardest food to a pulp so that it can be digested.

Sometimes the gizzard needs help. Then the bird swallows a few sharp stones along with his food. The jagged stones cut into the hard food, and this helps the tough gizzard to grind it to a pulpy mush.