I accidentally killed a cat at some point and now I'm in Verdistis and all the cats want to kill me. Is this normal? Perhaps they are crazy feral cats?

Ah, I did a quick Google search. I guess dogs and cats are part of their own animal faction and I'm a wanted man now. Perhaps this is good for others to know. I guess I'll be killing A LOT of cats from here on out.

Cats or dogs, I killed a wolf with a dog close by and got the same reaction. I save a lot in DD and load my last save before the misstep in order to avoid that annoying situation.

I just murder mercilessly anything that tries to take a bite out of me. Dogs included.

That works too !! . . . I believe if you kill pets that your reputation goes down a bit since the citizens frown on that sort of thing . . . =^ )

Bummer! I must have killed a dog at some point, because now I'm attacked by them. I didn't mean to do it and in fact didn't realize I had done it till I saw it as a trophy. Too late to go back now though.

Try not to kill any cats or you will be under siege . . . . =^ )
I believe Verdistis is the most likely spot to kill a cat by accident, in the grown up garden.

There's a dog in a room in one of the inns that will attack you if you enter the room. Kill that and all the dogs take umbrage and attack you afterward. I also accidentally killed a cat in the garden in Verdistis which seemed to annoy the other cats. The pets in the game are a bit protective of one another. Best to slaughter them and sell their bodies to a taxidermist store.