Why Does My Cat Go Nuts When It Spots Another Kitty?


Have you ever noticed your cat suddenly become alert, agitated, or even aggressive when they see another cat outside or through a window? Many cat owners observe this type of reaction and wonder why their furry friend is acting so wildly. Cats can have intense responses to spotting other felines near their territory. While it may seem perplexing, there are understandable reasons behind this behavior.

For example, imagine you are relaxing at home with your cat purring contently on your lap. Suddenly, your cat’s ears perk up as they notice a neighborhood stray strolling across your lawn. In an instant, your once-calm kitty is up and growling, with their fur standing on end as they glare out the window. They may even scratch at the glass or curtains in an effort to get to the intruder. It can be surprising to see your mellow companion turn into aggressive hunter mode so quickly!

In this article, we’ll explore the common reasons behind this phenomenon, including territoriality, excitement, redirected aggression, and breed tendencies. We’ll also provide solutions to curb the behavior, determine when professional help is needed, and ensure a peaceful, multi-cat home.


Cats are highly territorial animals that mark areas with scent (https://www.aspcapetinsurance.com/resources/how-to-deal-with-territorial-cats/). They use pheromones and urine to mark their territory and let other cats know that it is their domain. Even cats that live exclusively indoors can be very territorial over areas of the home that they perceive as theirs. When another cat enters an area marked by a territorial cat, it can trigger aggressive behavior as the resident cat tries to defend its territory.

Territorial aggression is often directed at other cats, but can also be directed toward people (https://vcahospitals.com/know-your-pet/cat-behavior-problems–aggression-in-cats-fear-and-territorial-to-other-household-cats). Some signs of territorial behavior in cats include urine marking/spraying, unprovoked attacks or swats at other cats, blocking access to areas like furniture or windows, and excessive vocalization when seeing another cat outside.

Perceived Threat

Seeing another cat can trigger a cat’s prey drive and defensive instincts. Cats are territorial animals and can view other cats as a threat to their domain and resources [1]. A cat who does not feel safe and secure in their territory will hide or may show aggression in an attempt to keep potential danger (other cats) away from them [1]. This reaction likely stems from your cat’s natural hunting instincts. They may see the other cat as potential prey or as a predator encroaching on their territory. Your cat’s aggressive reaction is their way of dealing with the perceived threat.

Territorial aggression can also occur when your cat sees another cat outside your home [2]. Your cat views the area near your house as their domain and will try to defend it from other animals. This territorial behavior is especially common between cats who live near each other but don’t get along. Even catching sight of a neighborhood cat through a window can trigger an aggressive reaction.


Some cats get very excited when they see another cat outside simply because it’s a novel and interesting experience for them. Indoor cats can get bored from the sameness of their daily routine, so seeing an unknown outdoor cat can provide some entertainment and stimulation. According to LoveMeow, “Seeing another cat who has the freedom to do everything they have dreamed of gets them all riled up.” The sight of the outdoor cat doing things they don’t normally get to do, like freely roaming, hunting, and exploring, can trigger their natural excitement and prey drive. It’s not necessarily aggression, but rather an enthusiastic response to something new and intriguing in their environment.

Redirected Aggression

Redirected aggression is a common cause of a cat appearing to “go crazy” when seeing another cat. This occurs when a cat becomes aroused or frustrated by a stimulus it cannot access, such as an outdoor cat it sees through a window. Since the source of frustration is out of reach, the cat redirects its aggression onto another target, usually a person or another pet in the home.

According to the Cornell Feline Health Center, “Common stimuli that trigger redirected aggression include loud noises, seeing an outdoor or stray cat through a window, or an altercation with another cat in the home” (source). The aggression is not random; the cat is frustrated by the presence of the outdoor cat it cannot access.

This reaction likely serves as a coping mechanism for dealing with a perceived threat combined with the inability to respond. Since the true target is out of reach, the aggression gets aimed at another animal or person instead. Redirected aggression in cats often targets owners, since they are frequently nearby when the cat gets triggered.

Breed Tendencies

Certain cat breeds tend to be more reactive and aggressive towards other cats compared to other breeds. One of the most reactive cat breeds is the Siamese. Siamese cats are known for becoming jealous of other pets in the home, which can lead to aggressive behavior when seeing another cat near their territory (Aggressive Cat Breeds: 9 Breeds That Can Be Grumpy). The Siamese breed tends to be vocal, energetic, and dominant, so they may react strongly when spotting an unknown cat near their home.

Other breeds like Bengals and Abyssinians can also be more prone to reactivity and territorial aggression. However, early socialization and training can help curb reactive tendencies in territorial breeds. With proper introduction and supervision, even typically reactive breeds like Siamese can learn to accept other cats peacefully.


There are several strategies that can help reduce territorial aggression between cats:

Distraction – Providing interactive toys and playtime is an effective way to redirect your cat’s focus away from the outdoor cat. Engage your cat in vigorous play with toys like feather wands and laser pointers when they start obsessing over the other cat [1].

Pheromones – Synthetic pheromones like Feliway can help relieve stress and curb aggressive behaviors. Use diffusers around the house and spray directly on areas where your cat sees the outdoor cat [2].

Counterconditioning – With positive reinforcement training, you can change your cat’s emotional response to seeing the outdoor cat. When your cat notices the other cat, reward calm behavior with treats to create positive associations [3].

When to Seek Help

While some cat behavioral issues can be managed at home, more extreme or dangerous behaviors warrant professional help. According to the ASPCA, signs that your cat needs veterinary assessment include “hiding and acting fearful, yoursing/growling at family members, urine marking/spraying in the home, unprovoked aggression, and not using the litter box”. These behaviors often indicate an underlying medical condition or significant stress. Additionally, if your cat is harming people or other pets, causing property damage, or engaging in compulsive behaviors, consult a veterinary behaviorist. They can diagnose the root cause and design an effective treatment plan which may include behavior modification, medication, and environmental changes.

Provide an Environment for Success

To reduce territorial aggression in multi-cat households, it’s important to provide a home environment designed for success. Cats are territorial creatures by nature and can feel threatened when forced to share their space. Providing adequate vertical space, hiding spots, and enrichment can help. As noted by the RSPCA, cats become attached to their home environment, so creating a harmonious space is key.

Vertical spaces like tall cat trees, shelves, and wall-mounted platforms allow cats to get up high and have their own vantage points to observe their territory. Hiding spots like cardboard boxes, igloo beds, and tunnel toys provide security. Rotating toys keeps cats mentally stimulated. Multiple feeding stations, water bowls, and litter boxes spaced far apart also minimize competition.

With these types of environmental modifications, cats can feel less threatened by having to share territory. It also allows them to separate themselves when overstimulated. A well-designed cat-friendly home can reduce territorial aggression and create a more harmonious environment for a multi-cat household.


In summary, there are a few main reasons why cats may act aggressively when spotting another feline. Territoriality and perceiving the other cat as a threat can trigger aggressive “crazy cat” behavior. Some cats also get riled up from excitement or as a form of redirected aggression. Certain breeds like Siamese tend to be more vocal and high-strung. While startling, this behavior is generally harmless between housed cats. Be patient, try redirection techniques, and ensure your cat feels secure in its environment. Most importantly, remember that this behavior stems from natural instincts. With time, consistency, and proper precautions, you and your cat can comfortably coexist.

With some care and understanding, cat owners can curb reactive behavior when spotting other cats. Stay alert to signs of stress in your pet. Provide a relaxing environment with vertical territory, like cat trees. Consider pheromone diffusers for anxious cats. Should problems persist, consult your veterinarian to rule out underlying issues. Remember, patience and compassion go a long way in supporting your cat’s wellbeing. With the right tools, your feline companion can thrive indoor alongside its fellow cats.

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