i too have noticed there is a distinct smell and taste from a good blow to the head, whether a fall or punch or collision with the dashboard, and it isn't blood, I've always called it the brain fluid tang.
wierd, i dunno what it is....
i fell on ice once, imitating sub zero's slide attack, hit a rock frozen in the ice and my head and feet traded places, whack!
it went sorta dark, there was a humming sound, i faw faint colored shapes drifting past from right to left if I recall, yellow triangles blue spheres green squares....after a few seconds my sight and hearing cleared and i realized the humming was people asking if i was dead or not....then.....the brain fluid tang taste/smell....
eta i also once sniffed the contents of an old drum at a mine to see what the liquid was, looked like water, it lit my ass on fire, i was blind and deaf and burning and freezing and then hearing (cows barking, if that makes sense) and seeing shit (tree stumps that were actually rocks) for a few minutes just from the smell, just one whiff, then a headache from hell for the next two hours....