The square-cube law is a biomechanical principle that explains why we don't have man-sized insects or elephant-sized birds.

As an object increases in size, its volume (and hence mass) increase as the cube of the linear size. The cross-sectional area of bodily organs such as bones, muscles, or breathing tubes only increases as the square of the linear size, however.

In other words, if you double the size of an animal, its mass increases by a factor 8, but the strength of its bones and muscles only increases by a factor of 4. Increase the size far enough, and the animal will no longer be strong enough to support its own weight. It'll also have trouble breathing and pumping enough blood around, because the tubes and blood vessels don't increase in size fast enough to handle the extra body weight either. (This is what prevents giant insects. Insects don't have lungs, they absorb the air they need directly from lots of small breathing holes all over their body. The small tubes that carry the air to the body tissues work fine at small sizes, but wouldn't be able to carry enough air at larger sizes.)

And of course a delicate balance like aerodynamic flight depends critically on these things.

First physics, now biology. You don't need any other comic to teach you stuff! What have you learnt from PvP today? Nothing, that's what!