Why Do Cats Hiss At New Kittens or Cats?

When scared or threatened, your cat will pull back her lips, bare her teeth in a menacing fashion and let out a puff of air that sounds like a hiss. This behavior is mimicry of a scary natural predator that most animals are afraid of -- the snake, according to PetPlace. Snakes are feared by most animals, so imitating this frightening sound is a great way to scare off predators or other animals that your cat fears, without having to get into a physical tussle. Although a hiss sometimes indicates that your kitty is about to attack the newcomer, it's usually just a warning for him to "back off" before she runs off.

When a cat hisses at a new cat or kitten, she is expressing a form of territorial aggression. Your kitty views your home as part of her territory, one that she must defend from any strangers coming into it. Not only does hissing convey aggression, a warning to "stay away," but it also establishes social order between cats. Your cat might hiss at the new kitty to let him know that she is the dominant cat in the house. This is especially true when a new kitten is introduced; your existing cat will want to establish herself as the older cat to be respected by the new little one.

When a resident cat hisses at a new arrival, it's normal behavior and usually nothing to worry about. Take the introductions slowly. Confine your new kitty for a few days, allowing the cats to smell each other under the door and on towels you rub on them. They should begin to stop hissing at each other's scents. Open the door to the confinement room and place a see-through baby gate at the door. Give them lots of tasty treats only while they are near each other and showing no signs of hissing or growling. You don't want to reward aggressive behavior by treating a cat that hisses. Once no hissing, spitting, growling or other signs of aggression occur, you can let your new kitty interact with your resident one.

When introducing cats, never punish one for hissing. This is a natural behavior -- both cats will associate the punishment with the presence of the other cat, delaying or preventing positive interactions between the two. While hissing usually signals to the other cat to "stay away or else," it can also be the precursor to an attack if accompanied by a growl or shriek, according to VetInfo. Before things escalate to this level, separate the cats until they don't respond to each other with any aggressive signs, including hissing. They might not become best friends, but at least they'll be indifferent to each other, without any hissing.

When spritzed around your home, products such as synthetic cat pheromone sprays can put your little ones at ease and make them more amenable to making friends. Spay or neuter both cats to reduce the chances of them fighting or hissing at one another; the hormones in an unfixed cat can trigger aggressive behaviors. Provide plenty of safe havens in the form of cat condos and shelves as retreats for each furball.