They butt heads

I mean literally, not figuratively.
They remind me of caribou or something.
Is it a dominance thing?  Are they just playing?  They aren't hurting each other but I've noticed them on many occasions, butting heads.

I haven't been able to catch the act with a photo, but it looks something like this

I'm learning that while behaviors are learned, some must be just deeply sewn into the culture of humanity.  More specifically, the culture of boys.  I am completely lost as to how to move forward with the boys and their new means of communication with one another.  I know for a fact they have never seen hitting or things like that but some things just come naturally I guess.  Mason gets frustrated and grabs the nearest appendage of his brother and BITES.  And William, whether as a defense move or just a new tactic, will grab Mason by the shirt and pull it over his head so he can't bite him.  Then they carry on like nothing happened.
I find myself wanting to laugh but also a little worried about how to discipline them.  They seem to figure things out on their own and they play so well together but sometimes I catch myself thinking, "Typical boys!"

William:

Notice his boots- he puts them on himself and just plays :)

Mason:

He fell fast asleep after the Children's Museum.  So cute.

My fabulous guys together:

W, M on a boys shopping trip

W,M
Aaron braved what I still haven't done alone: taking them out to eat.  It apparently didn't go very well so I'm not sure when I'll actually decide to try on my own...

William, Mason

When Aaron and I were giving them their bath the other night, we started talking about how the boys are already TWO and how much they have grown since we brought them home as teeny tiny babies.  I had to admit aloud that I haven't been able to picture them any older or bigger than they currently are.  I tried but I just can't!  They surprise me every day.  

Love,

Jessica