I adopted an orange cat from a rest stop. Yesterday, I adopted another stray gray cat that used to hiss alot. My orange cat would usually growl at the new gray stray. But yesterday something happened. The gray cat was laying on my lap. After my orange cat walked underneath the chair, the gray cat growled. The orange cat had its back to the gray and turned his head to hiss. The gray leaped on the orange's back and they fought. Should I still try to make them friends or should I leave the gray outside? It is obvious the cats doesn't like each other. They usually fight behind the window. And once before outside they fought in the past.