Warning Signs When Introducing Cats: 8 Issues To Watch Out For

Warning Signs When Introducing Cats

Getting a new cat is always exciting. But when happens when you’ve already got a cat? Will the two kitties get along? Learn to spot these warning signs when introducing cats to help ensure a peaceful and happy transition. 

Cats are pretty territorial creatures, being territorial and solitary is how they evolved to survive in the wild over thousands and thousands of years. Although your cat doesn’t live in the wild anymore, their brain still tells them to be VERY cautious of any newcomers.

And contrary to what we just said above, cats can also be pretty social. In order for them to be social you need to help reassure them that there is no danger with the new kitty that’s being introduced to their household. 

You need to know which warning signs to look for when introducing cats in order to help your current cat let their guard down and ensure a happy and healthy transition. 

Cats are very good about using body language to express themselves. They’re also good about reading the body language of another cat to see how the other cat is feeling. When introducing cats, body language warning signs is one of the first things you need to look out for. 

Your cat’s body language is a wonderful indication of the warning signs it’s trying to give the new cat. 

Their ears are flattened down

Warning sign when introducing cats: Airplane Ears
A cat showing "Airplane Ears" | Credit: @kinothemau

Believe it or not, your cat’s ears are very expressive. The positioning and mannerisms in how they move their ears is a great way to tell if they’re feeling happy, playful, anxious, threatened, or just about any other emotion a cat can have. 

When a cat’s ears are flattened down and sticking out to the side (AKA “Airplane Ears“) it can mean that they’re frightened or nervous. 

Airplane Ears is also a great indication that aggressive behavior is likely possible. 

If your cat’s ears are flattened and pushed back then your cat is essentially saying “Get back now!” 

Their fur is fluffed up

A cat’s fur does more than just keep it warm. It also serves as a great way for cats to express how they’re feeling. 

Whenever cats feel threatened they will fluff up their fur as a defense mechanism in order to make themselves look bigger than they really are.

Just about anytime a cat fluffs their fur up it means that they’re going into defensive mode. Exceptions to this rule are the cats that play roughly, usually younger cats or kittens. 

Their tail is flicking and moving

A majority of cat owners don’t know this, but the specific movement of your cat’s tail can indicate how they’re feeling. 

If your cat is flicking their tale around while keeping it somewhat rigid then it means they’re trying to send warning signs that they’re upset or scared. Cats also use this same tail movement when they’re hunting or stalking prey. 

Alternatively, if your cat is flicking it’s tail in a swishing motion, like how a flag waves, then it means they’re wanting to play. 

Their pupils are dilated

Warning signs when introducing cats: pupils
Non Dilated vs Dilated Pupils | Credit: @iyon.yy

Your cat’s pupils will dilate whenever they’re excited or surprised. One thing to note is that your cat’s pupils can dilate from both the fun kinds of excitement and from the stressful kinds of excitement. 

Pupil dilating should not be the only warning sign when introducing cats to look for. 

Behavioral Warning Signs

Whenever cats are feeling anxious, scared, threatened, or standoffish, their behavior can change. 

Knowing what behavioral warning signs to look for when introducing cats can help make the transition easier on everyone! 

Litterbox Aversion

Your current cat might start avoiding the litterbox whenever you introduce a new cat. They may do this out of stress, they may do it to be defiant, or they simply might not want to share the same litterbox as the new cat.

As a rule of thumb you should never have just one litterbox for two cats. (READ: How to introduce a cat to a new litterbox)

If your current cat or your new cat are refusing to use the litterbox and instead go elsewhere, you should NEVER scold them, yell at them, or try to scare or hurt them in any way. If the litterbox aversion doesn’t work itself out then please reach out to your vet for further guidance. 

Excessive Hiding

It’s no secret that cats love to find nice and cozy hiding spots. However if your current cat or your new cat seem to be hiding excessively then it means they’re scared of the other cat. 

This can be tough to gauge with a new cat because you’re not familiar with their behaviors and they will naturally be scared in the beginning anyways. 

Vocal Warning Signs

I’m sure you can already guess what the vocal warning signs when introducing cats are. But for the sake of being thorough we’re going to go ahead and list them anyways. 


Hissing is universal cat language for “I am scared, angry, or upset so please leave me alone.” What most people don’t know, however, is that hissing is normal 99.9999% of the time when introducing cats. 

You should only ever worry about hissing if it goes on for prolonged periods of time, such as multiple weeks after the cats have (slowly) been introduced to each other. 


Oftentimes hissing will be followed by growling. A low, rumbly growl is to be expected in the early stages of the introduction process. 

Whenever the pitch and volume of the growling goes up and turns into loud snarling or “yelling” that means that you need to take a step back and give the introduction process some more time. 

What is the latin name for cat

When Should I Intervene?

Depending on the breed, environment, and specific cat, the introduction process doesn’t always go as smooth as you had planned in your head. The cats will hiss, they’re both going to be scared, and it’s going to take some time to get them to be comfortable with each other. 

Oftentimes things will get out of hand and you will need to step in and intervene if you notice any of the following behaviors:

  • Loud shrieking or yelling
  • Biting (cats have bacteria on their teeth that can turn a bite wound into an infection VERY quickly)
  • Violent scratching (some light scratching is to be expected)
  • Fighting (more than just warning slaps)
Cats Normally Don't Breathe Through Their Mouths

Common Mistakes When Introducing Cats

Sometimes people simply don’t realize that introducing a new cat can be a long process. Actually, it SHOULD be a long process. Cats are very peculiar and you want to take things as slowly as possible. 

Here are some of the most common mistakes that cat owners make when introducing another cat:

  • They introduce them too quickly – New cats should be put into a room with everything they need for at least a few days. This lets your current cat get used to their scent and learn someone new is nearby.

  • Not being patient – Second to the safety of the cats, patience should be the top priority for you. Cats take time to adjust. You’re introducing a stranger into their lives and they need time to learn that this stranger won’t be a threat to them.

  • Yelling or scolding – Some (usually newer and inexperienced) cat owners will yell or scold the cats for hissing, growling, or fighting when a new one is introduced. This is terrible and will only add unnecessary stress to both cats.

  • Not enough litterboxes – We touched on this one above but it’s important enough to mention again. Two cats in the household require AT LEAST 2 litterboxes, preferably 3. 

  • Not monitoring them long enough – It might take a little bit of time before any aggression is shown. Don’t just assume after 20 minutes that everything is okay. Keep an eye on everyone!

  • Not paying attention to the warning signs – This is the most important one. If you know what to look for then you can tell when things are going to get bad before it happens!
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Are My Cats Getting Along?

Alright, you’ve made it this far.. the cats aren’t growling anymore, they’re eating, they’re using the litterbox just fine. Congrats, the hard part is over! The cats are tolerating each other, but how can you tell if they’re actually getting along?

  • Touching Noses – This is how cats tell each other ‘hello’ and allows them to communicate with their scents. Touching noses is a VERY positive sign that the cats are getting along!

  • Grooming Each Other – Cats build trust and show affection with other cats through grooming. If you see your old kitty and your new kitty grooming each other then it means they’re getting comfortable with each other.

  • Sharing is Caring – Cats are VERY territorial. If your cats are sharing things.. litterbox, scratching post, toys.. then it’s safe to say that they’re getting along. 

  • Sleeping Together – Cats show how comfortable they are with one another by sleeping or napping together. Cats that can let their guard down and fall asleep together are comfortable with one another. 
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