Lucy the cat likes food, belly rubs, humans, an occasional crumb of cheese and the other cats. (well, sorta.)
She does not, however, like the dog.
The staircase demarcates the boundary lines in the house - the cats live upstairs, with their food and box and access to many comfortable beds, and Jasper lives on the main floor, where he can see easily if there's anything nefarious afoot that must be doggily commented upon.
The cats come downstairs mostly late at night, when J's in his crate and they can sit on the windowsills and thunk! their tails and look out at the moonlit landscape and think catly thoughts, but there is an uneasy truce - the stairs are neutral territory. There is usually a cat or two lounging about halfway up, keeping an eye on things. Jasper pretends not to notice.
Today, though, he had an attack of puppy enthusiasm, and rushed up the stairs at Lucy, who was horrified (horrified!) to see the big galoot rushing at her and smacked him smartly a few times, swearing all the while.
Jas, of course, backed off momentarily, the wheels spinning in his head. Then he shook off any rational thought and plunged again. Lucy puffed up to raccoon size and smacked him again. He barked. She gave him a glare, fluffed up even more,
and chased him down the stairs.
Not bad for a cat who weighs approximately 1/10th of what he does.