The biting begins :/

mamatotwins0812

Need some help from veteran biter moms. One of my guys has started biting his twin, hard. I don't believe it's out of anger or playing, I'm pretty sure it's either frustration or simply 'just to bite'. Either way, it's bad. He got him 3 times on the back the other day and almost broke skin. Poor guy is still bruised today. Then just this morning he bit his arm. It's absolutely breaking my heart and I don't know what to do. I'm removing the biter and telling him firmly "no biting, biting hurts" and then consoling the bitten one but I just don't know what more I can do (and I won't bite back or hit or any of those suggestions). Any ideas?? TIA.