A human exiting a bathtub has perhaps a pound of water dripping off them—no big deal. A wet mouse, on the other hand, must lug around its body weight in excess water, and a wet fly is effectively pinned to the ground. The same action at different sizes produces massively different problems. “For every type of animal there is a most convenient size, and a change in size inevitably carries with it a change of form,” Haldane wrote. A most convenient size. A
