definalty a warning sign a big wide mouth full of sharp teeth would put anyone with any sense off, I've seen mine do it and then they start chattering so its a prelude to an all out attack, you might get some joy by gradually letting them spend time together in a neutral place, then its a case of watch and wait and be on alert some do take, one often backs down and lets the other be boss pig but not always, so its a matter of wait and see but be alert at all times never leave them alone, but as i say give them time together in neutral place and watch, if all goes well then try again but make sure they each have a bowl and water bottle and some where they can hide so they feel safe and then if theres nothing to spark off an argument you might be lucky, I've only got 2 pigs out of my 20 boys that will not share, so good luck,