Sad story, good question

I'll try to spare you all from as many disturbing details and just give what's necessary (although it's still a pretty awful story, so don't read on if you don't think you can handle it).

We have two outdoor 16-year-old cats from the same litter. They've shared a bed since day one and never fought. One was critically injured. Within seconds, the other cat swooped in, latched onto him, and helped finish him off, letting go after he went limp. I'd like to think this was some kind of mercy killing, an instinct to put his brother out of his misery. However, I think it's just as likely that he attacked his brother because he saw his erratic behavior as some sort of threat. Any cat behavior experts out there know for sure?

Oh my, that is a violent outcome . Honestly I don't know what to think of what you have described so far......There are so many questions. How and where was your kitty injured? Was he/she medically treated? Where did this happen? Was anyone present when it happened? As horrifying as they may be, more details about the injuries and subsequent attack are necessary to objectively relate or give opinion. I am so sorry for your loss

I have two males and they are the best of buddies. I believe if ever one suffers, the other one will try to end his best friend's misery, including mercy killing.

Cats in the wild (or in your case outdoors) will drive off or kill a cat that is ill. They are no longer of use to their "pride" and if they are so ill that they can't run off, then they can be killed. I have never heard of a "mercy killing" between cats.

I have had a lot of sibling cats over the years and one will start picking on the other if they are sick. Doesn't matter how close the bond is, it just happens. If your cat took it to the extreme that he killed his littermate, his brother had to be seriously ill.

Yes, cat do often mob or even assault their sick compatriot.

Although homecats are often comforting the sick cat-friend. But perhaps it is so only with homecats?


My next question is therefore. Cats "never" mobs nor assaults a sick human owner, although they otherwise use cat behaviour toghether.
And as most of us can witness, cats do often comfort their Ma or Pa when they are sick: they even often do it very efficiently!.

Sometimes they even comfort sick strangers. Feks cats working in retirements center, when they are lying themselves at the feet of dying olds, and thus give these dying olds peace on their last journey...

In another thread we discussed sound of distress, for example OYY. As some cats going to threw up can have.
I suspect ferales dont use these sounds - it would be too dangerous...
The only exception is the meowing of abandoned kittens - but this IS usually their last chance to survive.

Thus, although much of the behaviour cats - human is copied from their cat behavioral, much is apparently new, or very seldom occuring in the wild.

What do you others think??