Lily Suddenly Agressive w/Toshka?

I have 2 cats, Lily and Toshka, both have been fixed. Lily is a tigerstripe tabby who's very affectionate (lapcat, actually). Toshka is a very friendly white&orange "longy" manx. I adopted them together 3 years ago and after a few days they were like brother and sister; grooming and playing with each other with absolutely no problems. Lily doesn't like other "strange" cats that are in our neighborhood. However, this morning at 2am I awoke to hear Lily hissing at the open screened window in my bedroom where Toshka was looking out. Before I could fully awaken Lily attacked Toshka. I pulled Lily off Toshka and I attempted to calm her down but she broke free and attacked Toshka again (who was trying to run/hide from her). I managed to get a firm hold on Lily and calm her down and with the wife holding Toshka re-introduced them. Everything seem fine, they sniffed each other and Lily tried to groom Toshka while we were holding them both. We set them both down and everything seemed fine for about 1/2hr until they surprised each other in the bathroom. They both went bottlebrush and before we could react Lily attacked Toshka again so we decided to separate them for the rest of the evening. Later this morning Lily hissed at and tried to attack Toshka again w/o provocation. I've never seen this kind of Jekyll/Hyde behavior in a cat before and am hoping someone can provide an answer/solution to this problem. Thanks!...
Tom

This is called redirected aggression. Most likely there was another cat outside that your cats either saw or smelled. Seeing the strange cat triggered an instinct to attack those who invade her territory in Lily. It was not that Lily wanted to attack Toshka, but instead that the "attack center" in Lily's brain said to attack and Toshka was the only one around to attack. Occasionally this redirected aggression will cause the cat to attack their humans who just happen to be standing near when the attack signal is given.

So....what to do now? Lily's brain has now paired Toshka with the idea of intruder, so the attacks may continue. To make things better I would (1) keep the window closed. (2) Get some Feliway spray and spray it around the house or better yet buy Feliway Comfort Zone to plug into the wall. Feliway is a pheramone which mimics the friendly scent cats give when they rub their faces on things. It calms agitated cats. (3) Sprinkle a little vanilla on a wash cloth and rub both cats with the cloth. This will make both cats smell the same which will lessen the likelihod that Lily will attack. (4) start giving Lily and Toshka treats when they are together so that LIly will associate Toshka with happy things. Give lots of praise to Lily when she is around Toshka and being mellow. Put Lily in a separate room if she gets puffed up or growls at Toshka.

Hopefully these will work for you. Good luck!

Oh my,I hope things work out! Keep us posted,please!

After spending all day sleeping/resting while locked in my computer room (w/food, water & litter) Lily is acting a bit more affectionate/vocal like her old self. Brought her out for a few minutes to have some canned Tuna in the same room w/Toshka and while she looked at Toshka once or twice I didn't see any overt hostility. So, with a careful grip on Lily I let them touch noses and she didn't hiss, bottlebrush or make any attempt to get loose and Toshka didn't run away or act frightened. I didn't want to push my luck so I immediately returned Lily to her room where I'm visiting her now and she'll spend the night. Toshka's scent is all over me and that doesn't seem to bother her (she finds my lap as appealing as ever). This first step in reintroduction appears promising but I'll repeat this and keep them apart for at least a few more days rather than risk a repeat of last night's episode.
Tom
PS- Here's a pic of them together...

Update: I've been allowing Lily and Toshka to make contact through the slightly open computer room door (w/me holding the door & supervising) and both have shown no hostility/fear. Both try to get the door open wider by pushing/pulling on the door. Last night I let Lily out (closely supervised) and while a bit skittish while exploring the house (looking for the "intruder" cat?) she wasn't hostile or aggressive at all, even when Toshka would surprise her trying to get her to play. In fact, they even played a bit and lay down on the front room carpet about 6' apart grooming themselves. I locked her in the computer room again for the night and this morning let her out for a bit before going to work. All was fine (she nearly ignored Toshka) until she caught him eating her dry food in the computer room at which point she hissed and was going to chase him. Needless to say I put a quick end to that with Lily back in the computer room for the rest of the day. All in all the reintroduction appears to be going better than I'd hoped but it's apparently going to be *at least* a few days until we can trust Lily & Toshka together again for any real length of time. I'll probably try the first extended time together this weekend when I can be home all day to supervise.
Tom

It sounds like everything is going extremely well! Bravo to you for helping the two become buddies again.

It's now been 1 week since this unfortunate incident and I'm happy to report that everything appears to be back to normal. Toshka and Lily have been in constant unsupervised contact for over 24hrs now, playing & grooming each other again just as though nothing's happened. The window where the trouble started will be kept closed to prevent future problems. Thanks to everyone who helped with their advice and suggestions!
Tom