I have two cats, a brother and sister, two years old. They’ve always gotten along fine. Three days ago the male, Biscuit spent 24 hours at the vet because he couldn’t pee. He finally urinated on his own right as they were getting ready to sedate him for a catheter. So he’s been home for two days and ever since he got home, every time his sister Buttercup sees him she hisses and growls and runs away from him. He just ignores it. Just wondering if anyone has any insight as to why she’s acting this way? He was only away for 24 hours yet they’ve been together their whole life.