Moose the cat was from the shelter and I don't know his history. It is obvious, however, that he is not a fan of dogs. I think he's getting worse, too.
Moose came home when Shari was still alive. She grew up with cats and she never bothered with him. He would get under her sometimes and get agitated when she stepped on him (in her last year, she was arthritic and blind on the left side), though I know she didn't do it on purpose. When he got upset enough, he'd run after her and swat her (no front claws).
Almost six months after Shari died, I brought home Bear. Moose greeted him with a lot of hissing and spitting. Bear stayed away from him for a couple of months. Moose seemed compelled to "sheriff" Bear, though. Moose followed him around and would swat at him if he perceived Bear as being out of line (like Bear chasing his own tail or me raising my voice to Bear). Things settled down after a few months, with both giving each other space.
So about six weeks ago, Moose started getting excessively agitated with Bear again. One evening I was putting Bear out back with a marrow bone and Bear was barking excitedly and dancing around a bit by the door. When I opened the door to let him out, Moose came up behind me, went in between my legs, and tried to attack Bear. I ended up with a very nice bite wound in my calf that went through my sweat pants. I still have the mark from it. Then the other night, I let Bear in the house and Moose ran up behind him and bit his ankle hard enough to make Bear yelp. Today at lunch time, everyone was getting liver treats. Bear was in the kitchen about 10 feet from the cats and I tossed a treat to Bear, which hit the floor. Moose promptly leaped off the cat tree and pounced on Bear's head when Bear was trying to find the treat.
Should I be concerned that Moose has something going on health-wise and get him checked out? Or is he just that agitated and afraid of the dog and perhaps some Rescue Remedy or maybe that Feliway stuff would help?
It might help to know that Bear is crated when I am not home and I do not allow him to chase the cats (even when they tease him). I do not leave them alone together unsupervised.