My cat suddenly attacked her sister, hissed, and hid. What happened?

The first thing I would do for now is put Attila in a room by herself with a litter box, food and water bowls, comfortable resting places, etc. and leave her alone for the next few days apart from coming in briefly to refill her food and water and change her litter. When cats become upset and aggressive like this, for whatever reason, it can take up to a week for them to fully calm down and return to normal - until then, it's best to leave her completely alone and give her plenty of space. Some cats can have serious aggression issues that are triggered by a strange or scary noise, an unusual smell, or anything else that startles them. It's possible that Attila may have had a scary dream that frightened her, or she could be painful due to a pinched nerve, arthritis, or some other issue that may have been aggravated by petting. If she calms down over the next few days and things return to normal with no further problems, you may not need to do anything else. If she is still acting aggressive a week from now, or if this becomes a recurring problem for her in the future, I would strongly recommend making an appointment with a veterinary behaviorist - he/she can evaluate Attila in person and help you determine what may be triggering these episodes, and will also give you some specific suggestions for managing her when this happens. Prescription medication is helpful for some cats with aggression issues, so this is something that could be discussed also. You can search for a board-certified veterinary behaviorist in your area here: www.dacvb.org

Thank you for submitting your question regarding Kitty Mucher. If she spends time outdoors, then I worry that she sustained an injury. Cat bite wounds are common and could explain her abrupt change in behavior. If she is not acting normal by the time you return home today, then she will need to see her veterinarian. If she does have a wound (and they can be hard to find), she will require treatment. I hope this information helps!

It may be due to illness or injury. It can also be redirected (or displaced) aggression. This is when one cat is unable to directly respond to a perceived threat and "vents" on whoever is closest. This is usually an owner or another pet. Never handle or grab your cat if she is displaying aggressive tendencies. This can lead to a serious bite or scratch. Schedule an exam with your vet to rule out medical causes. If they are indoor cats, provide a ' cool down' period by separating them. Keep stray or strange cats away from windows or doors and out of your yard. Control what your cat sees by closing doors or drawing the blinds. Consider using pheromone products to decrease anxiety/stress level in the house. Search www.pet360.com for pheromone products.

Cats will often do this if they have been separated for a period of time, especially if one cat looks or smells different - your female cat may have strange smells on her from her time outside. Most of the time, this reaction is mild and the cats will get along again after a day or two. If there is any serious fighting or if his aggressive behavior towards her does not seem to be improving, then you may need to separate them and gradually reintroduce them to each other - feel free to ask for additional help on this if needed :)

Poor girl! There could be something that has spooked her. Or she could be not feeling well. Or there could even be an internal conflict with another cat in the household. The first thing I would do is make sure she is healthy. I would see if your vet can look at her and make sure she isn’t painful, no infection, no fever, no urinary tract infection, etc. if she isn’t feeling well, this definitely can cause a change in behavior. If everything is normal then I would make sure she is getting along with everyone in the house. Make sure there are plenty of litter boxes as this is something they commonly will become territorial over. You can even put out some feliway diffusers which are pheromones they help calm down cats. Unfortunately these don’t work on everyone. You make also look into vetriscience composure treats as a natural calming supplement. I hope this helps!

It's possible the stress of your being gone caused the behavior change. I would give Hippy a few days to rest, relax, and make sure she can get to her food, litter, places to hide, etc without being bothered and see if that helps. Sometimes, pain or underlying illness can also cause a cat to suddenly lash out and hiss or swat at other cats, so if the behavior continues or you see visible signs of illness, a vet visit to rule out health issues is best.

Cats exhibit this behavior sometimes when one leaves the house. Most of the time it’s more growling and hissing and running then anything else. Most cats will get over this quickly. Supervise them so that they don’t hurt each other and make sure one does not bully the other. If you have something they really like it such as canned cat food, you could try feeding both cats the food or treats close to each other and talking sweetly and petting both. I hope this helps and best of luck!