As he drew out his knife again and proceeded to skin the snake, he continued, "I don't believe in killing snakes as a general rule, but blacksnakes do more harm than good, I believe. It's true they kill rats and mice, but they also eat birds' eggs and young birds and squirrels, and no end of other useful creatures. And they are so active that one snake will kill a great number in the course of a year." "I don't understand how they can eat anything so big as that young squirrel," said Lew, "but I know they do." "Really they don't," laughed Charley. "They drag themselves outside of their prey. You know their jaws are loose so they can spread them, and their teeth point backward. What they do is to work the upper jaw and then the lower, hooking their teeth into their food, pulling back with each half of the jaw in turn. You see they literally pull themselves over their prey. Well, I'm glad we got that fellow. I suppose it's my business to kill all the blacksnakes I can. Whatever harms the squirrels, hurts the forest." "What do you mean?" asked Lew. "Why, you know that squirrels help to plant the nut trees in a forest. Some tree seeds, like pine and maple seeds, are so small or light that they are carried easily by birds and winds, and so scattered about. But acorns and nuts are so heavy that they fall straight down to the earth. If the squirrels didn't carry them away and bury them in such quantities, how could we ever have had these great stands of nut and oak trees?" "I never thought of that," said Lew. "It looks as though what Mr. Marlin said was right--walking about through the forest is only a small part of a forest guard's work. He's got to know an awful lot about things before he can be sure just what he ought to do." "I never had any idea how big a job it is, Lew. And think what a forester must have to know. I tell you it takes a man to fill a job like that." Noon came. The boys grew hungry. "I could eat all the sandwiches we have myself," smiled Charley. "I wonder if we couldn't catch some trout to help out. It would be all right to make a fire over here, I'm sure. And we'll keep it so small it won't make any smoke. And even if it did, it couldn't possibly betray the location of our camp." They made their way to the stream in the middle of the valley, baited their hooks, and dropped them into the water. In no time they had half a dozen fine trout. "You clean 'em, Lew," suggested Charley, "and I'll make a little fireplace." He selected a little shoulder of earth close to the run and began to dig into it with a stick. In a moment he had uncovered a deposit of solid clay. The clay was hard to dig, but he could shape his fireplace in it exactly as he wanted it. When the task was completed, he started a very small fire with leaves and small branches. By careful feeding, he kept the flames burning clear, with almost no smoke. Presently he had a bed of glowing coals that almost filled the little fireplace.