We have two kittens we adopted 3 months ago. The male cat is some variation of Russian Blue and is neutered; the female cat (2 months older but smaller) is orange and not spayed (yet).
Whenever we play with toys (rat on a string, springs), the male cat would always get (too?) aggressive. He would growl whenever he gets his toy, but then escalates to hissing and swatting at the female cat when she comes closer.
From the linked post, it seems like growling is normal behavior, but when it gets to hissing, should I intervene?
One time, the week when they just got adopted, we found her nose bloodied. A few weeks later, we found a wound on his feet. But they seem to be best buddies with each other. So should I just leave them be (even if they physically hurt each other sometimes)?