As a person who took a metal sign post to the side of the head as a kid (wearing a helmet) I can vouch for any of these, I walked away somewhat dizzy with a stiff neck and a couple broken teeth and a popped out shoulder, would've been a hell of a lot worse! Basically (as much as I can remember anyway) some dog ran into the side of the front wheel of my mom's motorcycle.
Don't use bikes, he says.