I have two castrated male cats, six and five years old. They had always gotten along beautifully until a few weeks ago, when they suddenly began fighting. Now every time they see each other, they hiss, attack each other, and then run away. There is no indication that their behavior is getting better. What can I do?

This is the third part of a five-part article on aggression between cats. This week I will focus on fear-induced aggression.When two cats in a household who have gotten along well together suddenly become aggressive toward each other, the problem is generally fear-induced aggression. Neither of the cats seeks the other out, but if they run into each other, both will act startled and attack. Usually this problem begins by mistake or by accident, according to "Aggression Between Cats," published by Purina.

For example, Cat A may be sitting in a window as an outside cat walks by. Cat B, who is territorially aggressive toward outside cats, is in the middle of the room. Cat B sees the outside cat and rushes toward the window to attack it. Unfortunately, Cat A happens to be in the way and sees Cat B aggressively charging toward it. Cat A puffs up and hisses. Cat B redirects its attention to Cat A and puffs up and hisses. Then the cats attack each other. Each acts as if the other started the fight.

The Quaker Pet Care Center provides another scenario that can occur to cause aggression: Two friendly cats may be resting when a frightening incident occurs, such as a bookshelf falling over. Both cats become startled, puff up and assume defensive postures. When they see each other in defensive posture, they act as if the other is about to attack. Consequently, each reacts defensively, a fight ensues, and thereafter they are aggressive whenever they see each other.

This type of aggressive behavior can be treated successfully. The cats must get to know each other all over again without either cat becoming afraid or aggressive.

To begin this process, the cats should be separated so that they cannot see each other except during treatment procedures. One way to do this is to expose them to each other for prolonged periods, but in such a way that one cannot get to the other.

Purina makes the suggestion of keeping them in large cages at opposite ends of the room, where they can see each other, but cannot escape; or, the cats could be kept on leashes or in harnesses and kept apart but within sight of one another. After several hours, they might be brought closer together. After many such sessions, it should be possible for them to be next to each other, where they might groom or play together as they did before; then they could be let loose.

Holiday alert - Don't be tempted to share your holiday feast with your pet. Bones, especially from poultry, can injure and even kill your pet. Stick with your pet's regular food, and if you must give him treats, feed him the kind made specially for him - from a pet store or the pet section of your supermarket.