But at the same time love each other?!
My two (10 month old boy and 13 month old girl, both neutered) drive me up the wall, rolling around fighting, nipping each other, etc. their howls genuinely make me panic that they're actually hurting each other, but of course they bloody aren't!
They hide round corners when they hear the other coming, so they can leap out and scare them...
They biff each other and yowl when biffed in return, then run and lie 18 inches from their offending pal, legs akimbo, as if to say 'pleeeeeeeass don't biff me again, wink wink nudge nudge!!'
They bump noses ALL the time. I'm really hoping this means they love each other really! 
And the funniest thing is, Scabbers has claimed a transparent plastic tray that I left on the floor, as his "new bed" but every time Millie walks in he ducks down to hide in the trag, not realising she can clearly see him through the clear plastic!
God I get too much amusement from my babies!!