Why do my fingers hurt when i hit them with a hammer?

Answer 1

All your flesh has capillaries and veins that carry fluid. Everytime that you damage your tissue (smash it with a hammer) you break open some of the fluid carrying "highways." The fluid "floods the countryside" and your poor thumb starts to swell up.

Answer 2

Because You Are Hitting The a Object of Your Body. Such as if you were hitting other places. legs,arms ECT