You're sitting next to a purring cat when he rolls over with his belly pointed up. You reach in to rub his tummy, but instead of appreciating it, he attacks your hand instead. What just happened?

Some cats don't like belly rubs. Why? Mainly because the stomach area is a very sensitive part of a cat's body. This soft underbelly protects some of their most vital organs, according to the South Boston Animal Hospital.

In addition, the hair follicles on a cat's stomach and tail are "hypersensitive to touch, so petting there can be overstimulating," Lena Provoost, an animal behaviorist at the University of Pennsylvania School of Veterinary Medicine, told National Geographic.

If a cat shows you its belly and seems to want affection, try scratching under the cat's chin or around the cheeks. If you're not sure if the cat wants a belly rub, slowly reach your hand toward the tummy and gauge the cat's reaction. If the cat reacts angrily and try to grab or claw your hand, don't try it again. This is an instinctive reaction — try not to take it personally.

If they don't react, you're likely clear to proceed.

Why cats show you their belly

This cat isn't a fan of having his belly rubbed. This cat looks like he's ready to attack the hand that's petting his belly. (Photo: Steve Heap/Shutterstock)

When a dog rolls over and shows you his belly, it's often because he wants attention. There's a good chance he's asking you to rub or scratch his tummy. So naturally, when a cat does this same behavior, people assume it's for the same reason.

But that's not true. When a cat shows her belly, it's a way to communicate one of four things. You'll likely know which mood your cat is expressing by reading other behavior signals.

1. She's relaxed and trusts you a lot. If she's relaxed, she may purr or rub up against you. She be sleeping and may show you her belly as she stretches or changes positions.

2. She's playing. Relaxed also can mean playful. For example, she may go belly-up to have all of her paws free to bat at her favorite toy.

3. She's feeling defensive. Turning over on her back gets her best weapons out front: the teeth and all of her claws. You'll be able to tell if your cat is upset — she may flatten her ears or make growling or hissing noises.

4. She's in heat. If you have a female cat who hasn't been spayed, this may be mating behavior. It's a sign of affection to a potential mate. It's probably best to leave her alone until it passes.

Angela Nelson ( @bostonangela ) is an exhausted mom of two young daughters and two old cats, and a Pulitzer Prize-winning digital editor with more than 15 years of experience delivering news and information to audiences worldwide.

Why some cats hate belly rubs
The science behind why some cats hate belly rubs, plus what it means when a cat rolls over and shows you its belly.