J.W.
My third got angry because we wouldn't let him go out and play when he was two. To punish us he headbutted the door knob, yeah, I don't follow the logic either. Anyway it was almost six months before the lump went away. I asked his pediatrician about it at his check up. He said hard bumps to the head cause calcification not unlike what happens with a broken bone. Just the body protecting his head. Depending on how hard the bump it is reabsorbed into the body and goes away. For Andy it was six months, he really punished us. :-/