Originally Posted by StefanZ
You described here a situation. Take a note book, and try to write down these situations where he hisses. Like you did here.
So you will surely see if there is a pattern.
Good luck and much pleasure with your ethological study!
There is definitely a pattern. When Moose gets cranked up, that's when he's more likely to hiss at her, and only her, not my other cat. When he's in one of his "moods", and she approaches, or walks by, he'll hiss. He's also run up to her, hissed and ran away. Nothing ever comes of it; if she could roll her eyes, she would.