Mary Zarinelli, age 11, of St. Genevieve, Mo., for her question:

Why do snakes change their skins?

Most snakes live their lives on the ground, crawling over grubby soil and gritty sand and scratchy grasses. Such wear and tear is hard on the clothing. The snakes wear a tough and scaly skin, but after a while it becomes worn and torn. He may need to change once a year or oftener. Meantime he grows a new skin under the old one and when all is ready, the old one is shed.

Shedding is the hardest part of a snake's life. He has no arms or legs to help him wriggle out of his old, tight skin. As a rule, he rubs himself against rough stogles or grasses, but the difficult job takes time. When it is done, he is very happy to leave his old, worn skin behind.