I have two cats. Our older cat Moose, and our younger cat Marshall. Just yesterday when I came home from school, my dad said Moose was hiding in our basement after he and Marshall had been fighting all day. Our cats fight sometimes, but this time it was actually violent. I got Moose out of hiding, but after about a minute, Marshall attacked Moose. My mom and I eventually separated them, but Marshall kept making this weird humming sound he makes when he is angry. Moose was shut in the basement last night to keep them from fighting and Marshall slept upstairs. Tonight Marshall sleeps in the basement and Moose sleeps upstairs. Even after we let Moose upstairs, he seemed freaked out and tense. I don't know what is going on with them. My dad said a cat that lives a few doors down walked through our backyard, we don't let our cats outside, but Moose gets very angry if any animals bigger than a rabbit come into our yard. My mom thinks Moose took his anger out on Marshall, but is unsure why the fighting continues. They have fought like that before, but it usually stops after one time. Has anyone had any pet issues like this? I could really use some advice.