Calvin the reptile is in trouble. As an ectotherm, his body relies on the environment to warm or cool its temperature. Since it's colder outside, Calvin's body temperature falls and he becomes sluggish. He'll go into torpor if he can't find a warm place to lie. Mom tells Calvin to leave the thermostat alone and put a sweater on if he's cold. Calvin, slumped on a chair, says he doesn't have the energy.