Bites

The boys are going through a phase apparently where they like to bite.  Mainly each other, but every now and then they will bite one of us.  It actually worries me since they will be playing and just randomly bite the other one and they will fuss at first - as in to say "ouch that hurts", but then they both start laughing and will do it again.  These aren't little bites either like when they are teething.  These are break the skin leave bruises bites, and here they are laughing about it and doing it to each other on purpose since they think it is funny.  Is that normal?  I don't think it is.  Hopefully they will grow out of it soon!  We even find random bites on them - I found one on Thing 2's leg the other day and on the side of Thing 1's face.  I ask'd Nathan - do you know how he got this?  The answer is "no".  How do we not hear them screaming in pain or anger?  I'm really ready for the biting phase to be over!