Strange biting

Ok, I got my first corn snake 6 weeks ago. I normally know much about snakes and their behavior, but mine is doing something I really don`t understand. He is very friendly, and I can pick him up, touch him, let him out to walk around the room then pick him back up without a problem.
A few days ago, I was laying down and I had him on my, he was doing the regular things going up down and around. Then he when to my neck and I saw him with a mirror opening him mouth and trying to bite me on the neck without any reason. I moved his head, he didn`t try to bite my hand, but he keep wanting to bite my neck (really weird).
A week before that, he was crawled under my t-shirt and after a while of sitting there, I saw him trying to bite the side of my stomach. And before that he gave me a little bite on my stomach, like really gently for a second and let go. In all three of the occasions he was not provoked, not scared, and he didn`t act aggressive or react to as he`s biting prey.
Does anybody have any idea what he`s doing???