Why a Cat's Pupils Get Big

According to the Arizona Humane Society, a cat's pupils can widen out of pure surprise. Perhaps your cat is stealthily walking around your home at night, thinking she has the whole place to herself, and all of a sudden you show up right behind her. If you notice her pupils suddenly widening, it's because she wasn't expecting you. You surprised and startled the poor thing.

Big pupils in a cat might also point to abject fear. If her pupils are slightly widened, then she's slightly scared. If they're severely widened, she's absolutely terrified. Perhaps your cat spots your neighbor's large and imposing dog through the windows, and she's worried for her life that he's going to somehow get to her and attack -- yikes.

Bigger pupils can also mean that a cat is in a state of anxiety and nervousness, and perhaps that she doesn't know what to do with herself. If your cat's pupils are especially large, pay attention to other key signs of anxiety, including a rounded and hunched body, a tense tail and a lowered head.

One common source of pet nerves is a trip to the veterinarian's office. You might notice your cat's pupils gradually widening as she sees you take her carrier out from hiding in the basement -- uh oh.

Large feline pupils can also indicate that your fluff ball is on the defense. She feels threatened and intimidated by something and doesn't like it one bit.

Be very cautious in these instances. A defensive cat is often a cat who is ready to protect herself. Don't be surprised if defensiveness quickly turns into aggression -- biting, scratching, the whole nine yards. If you suspect that a cat is in defense mode, for any reason, leave her alone and let her cool off.

If a cat bites or scratches you or someone you know, get medical help immediately. Bites and scratches from cats sometimes lead to dangerous infections, so play it safe.

Although it might seem otherwise, dilated pupils aren't always a bad sign. According to the National Association of Professional Pet Sitters, wide pupils can also mean that a cat is feeling enthusiastic and excited about something.

Perhaps she senses that you're about to play with her. Maybe you just picked up her favorite stuffed mouse and she can't wait to chase after it. When it comes to deciphering feline emotion and mood, context is a great friend.