Stuck on Earth

Ketchvar III's mission is simple: travel to Planet Earth, inhabit the body of an average teenager, and determine if the human race should be annihilated. And so Ketchvar--who, to human eyes, looks just like a common snail--crawls into the brain of one Tom Filber and attempts to do his analysis. At first glance, Tom appears to be the perfect specimen--fourteen years old, good health, above average intelligence.