Cats hiss and growl when they're either feeling disturbed or threatened by something. It's a type of verbal warning that the animal gives off before it takes further action. While it may appear that cats are hissing and growling at nothing, cats only do this when they feel there is a problem. So while you might wonder what's wrong or search for the source of a problem, it's important to know that these actions could be provoked by a variety of things and aren't necessarily directed at you.
If your cat is hissing and growling, but appears to be staring off into space, check to see if it might be looking out a window at something outside. Oftentimes, it will have its eyes locked on birds, squirrels or some other object that's moving around your yard that either interests or scares the cat. Birds, for example, are a common cat prey. The hisses could turn to "cat chatter," which, according to the website CatStuff, is mimicking a bird's chirp in order to lure it.
It Is Upset
Cats aren't typically perceived as social animals, at least to the extent that dogs are. But cats need love too. One reason why a cat might hiss or growl is because it's upset with its owner. This could occur after the owner returns from vacation, for example, and the cat is angry that it has been left alone in the house, aside from someone checking in to feed it. Hissing and growling could be the animal's way of voicing its displeasure. In a situation such as this, the animal will eventually come around and behave the way it normally would after it gets its point across.
Reaction to Pain
If your cat hisses or growls when you pick it up or pet it, it could be a sign that the animal is in pain. According to the ASPCA, pain-induced aggression can occur if the cat has been injured or suffers from arthritis, dental pain or another serious disease. The cat may even hiss or growl when you approach it, in anticipation of being handled. If this is the case, take your cat to a veterinarian to find out if there is a physical condition causing your cat to lash out.
If you've just got a new cat, any existing cats may take exception to it. Hissing and growling is a way for the existing cat to show the newcomer exactly who is boss. This may escalate beyond hissing and growling into cat fights, until boundaries are established. However, this hissing and growling can also be directed toward cats in more less obvious situations. For example, if a house cat senses a stray cat wandering outside nearby, it may react similarly.