I recently got a pet rat from a friend as a present, and I already had a pet rat, they are both male, and I took my time introducing them, now they're in the cage together and sometimes fights break out, and the new rat SQUEAKS loudly whenever i try to pick him up. Also my old rat has been attacking the new one, he actually bit the new one and broke skin, so i seperated them for a while, now they are back together, it's is much more calmer, do you think with time my rat will get use to the new one? what should i do, i don't want either to get hurt!?