My indoor cats, who have been friends for 3 years, had a "mysterious incident" and now have decided they no longer like each other. I believe what happened is they saw another cat or dog outside from a window and scared one another. Now they hiss/growl and stare down each other. I've been following the appropriate steps for introducing two cats (keeping in separate rooms, scent swapping, room swapping, feeding between closed door and graduating now to a blanketed baby gate, brief play sessions on opposite sides of the room, playing under the door). I purchased a ton of cat toys, pheromone and calming sprays, a tall tree to play on, ect. But progress is slow going and every hiss makes me less and less hopeful that I'll be able to mend their relationship.
I was wondering if anyone out there had experienced this sudden fighting between their cats? Or if they could recommend their tips for introducing two cats, I would be very grateful.