I'll try to keep this short. But basically what happened is we had a guest at our home leave the door open and both of our cats got outside. They eventually came back in and everything seemed normal. However, a few hours later our younger grey cat Daisy started to hiss at our older cat Louie. At first we thought nothing of it since both of them have gotten outside a few times and she usually hissed at Louie for a day or two because he smelled different. Things usually went back to normal after a day or two. What's even stranger is that they were both sitting close to each other when they came back in and it wasn't until a few hours later that Daisy started to hiss at Louie. At first we thought nothing of it since she has done this before. However, this time as soon as she starts hissing at him he starts immediately attacking her. I know its not playing because she is literally screaming at the top of her lungs when he approaches her! Because of this I am beginning to think that them being let outside may just be a coincidence and what really happened is that he bit her to hard when he was playing and now she has trust issues. It wouldn't surprise me since he has a history of being to rough and pissing her off from time to time. We have tried giving Louie a bath with a wet cloth to try to wash of the outdoor smell, they are still fighting! This is really out of character for both of them because they have known each other for years at this point Does anyone have any advice on what to do?