Help with my rats!!!?

I have 2 pet rats, Phineas and Ferb. Ferb died recently so I bough Phineas a friend so he would'nt be lonely. I named him Zeke. He is a little bit smaller and younger than Phineas. I put them together in a small cardboard box and they seemed to get along fine, but then I put them in the cage and they got along for a few minutes, but then Phineas bit Zeke! What will I do? What will hapen? Will Phineas kill Zeke? Help!?!?