Weird sibling cat aggression problem

rhymenocerous

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Hi! We need some help, long post incoming.

We have two tabby cats, brother and sister. I think they're 13 or so years old, we got them both when they were a few months old from the same litter. They were spayed / neutered a long time ago.

Now the problem we have is this. The brother, for whatever reason, will go into this odd trance and get very aggressive. I've only seen it myself two or three times but my mother has seen it a few times too, so i'll be adding what she's seen.

What he does is he will start shaking sort of violently, around his back legs i'm told, and then go into a crazed sort of trance which you can't really knock him out of. Then he'll lunge for his sister's neck and clamp down on it. She obviously doesn't like this, so she complains, and if you try to stop him he'll growl. Then he'll sort of mount her, but it doesn't appear to be a sexual kind of thing, but it looks more of a "hey i'm big and angry and i'm gonna stand on you to show i'm the boss" sort of deal. A couple of times i saw him stomping down on one of her legs with his own leg, but they may have just been him trying to put his foot in a more stable position to better assist with whatever foul mission he was undertaking.

Once this happens we're usually able to separate them, at which point he'll have snapped out of his trance and will probably start licking himself or some such nonsense. There's no signs of embarrassment or anything, and he gets embarrassed a lot, like if he falls off a basket of washing or something he'll show obvious signs of "you didn't see that!".

We've never seen anything remotely like this before, and i'd say 99.9% of the time they're the same lovable mongrels we've had for 13 or so years, it's just a few times it's like he's being possessed. In fact he's lying down right next to me after being patted to death. Adorable right now

But pure evil when he does this weird behavior.

Any aggression is the typical adorable playfighting stuff which results is nothing. They often sleep together and groom eachother and the like, so i'd say they have a good cat sibling relationship. They're both also very affectionate toward us, although rather skitty when it comes to being held, after a short amount of time (20 seconds if not sooner) they'll try and escape. I dunno why they never liked being held, oh well.

For all we know they're both perfectly healthy at the moment also.

Perhaps coincidentally or not was the recent death of a third cat which we named Mirri (he was old and had a blocked bladder and had to be put down). He was a stray who ended up choosing our home to be his home about 8-9 years ago i think. Our two would always pick on Mirri, they never got on with him, but had mellowed towards him a lot in recent years. 3 years ago if they saw him they'd hiss at him and potentially fight him, but since then they would even sleep on the same bed (during winter). Nothing more than that tho.

We *think* that Mirri's departure roughly coincides with the start of this ridiculous behavior.

There's very little variation in what he does. It's pretty much the same crazed trance and biting / mounting sequence every time.

So i'm at a loss. Any advice or information would be greatly appreciated, this is quite disturbing
 

momofmany

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My guess is that you have 1 of 2 things going on. Even though the relationship wih Mirri mellowed over the years, there was still tension with him that the brother has now redirected towards his sister. I've seen very odd things happen when one of the resident cats die, and many times its things you never expected.

Secondly, could this be a cognitive disorder? Cognitive disorders could be caused by things like strokes, brain tumors, kitty "alzheimer", etc. I've had older cats with the problem and it often changes their behavior in very odd ways.

Have you had a complete geriatric workup on your cats lately? It's recommended that you start doing this around 10 years old (baseline) and at least annually after that to monitor for changes. Any drastic behavior changes in cats should be seen by a vet to rule out medical reasons.
 
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rhymenocerous

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Hey, thanks for the reply


We haven't given the cats any geriatric type testing at all i don't think. A few months ago he got badly scratched on his chest (we think major cat fight), so he went to the vet and whatnot. Actually it wasn't a vet, as much as it was a cat fanatic (she sounded awesome!), but odds are she didn't do any testing beyond that pertaining to the chest wound.

I'll definitely pass this information on to mother tomorrow and we can work out what to do. We have suspected he might be getting a tad senile, albeit jokingly, but if this is potentially more serious then i think we'll definitely have to get him at least checked up.

Thanks again!
 
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