This type of aggression may rear its fuzzy little head when a cat reaches social maturity. It can be directed toward animals or people and it may be demonstrated toward specific cats in the home but not toward others.
When a new cat is introduced into a home where there are existing cats, you'll often see territorial aggression. It can also occur between longtime companions when one cat returns from the veterinary clinic, because the unfamiliar, and definitely unpopular, scents can make him smell like an intruder.
Territorial aggression can be exhibited in various subtle ways. It may happen in your home without your even hearing a hiss or seeing a paw raised. For example, a dominant cat may block access to the litter boxes or the food bowl, but it may look to you as if he's just casually lounging in the doorway. You may not have an idea this blocking behavior is taking place until an inappropriate elimination or spray-marking problem becomes obvious.
• Treatment plan
Reprinted from Cat vs. Cat: Keeping Peace When You Have More Than One Cat by Pam Johnson-Bennett © 2004. Permission granted by Penguin Putnam.