Cat rolls over then nips

I'm confused. We have had our cat for about a year. He was 5 yrs. old when we got him. He is very friendly and talks all the time. He wants to be around people all the time. Here is the confusing part. When we pet him, sometimes he will turn over on his back as if to ask us to scratch his stomach, but when you do he takes his paw and tries to bring you in and then then gives a little nip on your hand or arm.
It's usually not too hard but sometimes it does leave a mark on your skin.

Sometimes his ears go back and he looks a little wild. Almost like a Jekyll and Hyde thing.

Is that his way of telling you he loves you or telling you to stay away, no more?

It's absolutely normal - hardly any cats will let you scratch their stomach at all, and most grab onto your hand with all paws and try to kick it with their back feet! They do it to each other, and to prey, and toys, and it doesn't mean anything terrible, just a natural reaction.

I should have been more clear regarding our cat rolling on his back and then trying to pull us in with his paws to get a nip. He will do this even if "HE HAS COME TO US for attention"
We will pet him and he rolls on his back. We then pull back because if you have ever been bitten you know you never want it to happen again! We wonder why he does this and are worried that a guest may mistake this for him wanting a belly rub. Someone getting bitten is a real fear.

One of mine does that as a game. I've found if I don't pull my hand away, it doesn't leave mark. We call her "the beartrap." She lays there still on her back, until you rub her belly, then the trap snaps shut on you.

Ferris does the same thing and it is SO hard to resist touching his little belly, but it overstimulates him, and then he grabs your hand and nips, just as a stimulated male cat would do to a female cat.

It's just natural behavior, and if you don't pull your hand away, he won't think it's more of a game and bite harder.

I just try to remember that it is belly rub at your own risk. You'll just have to warn your guests, is all.

Actually it is a normal reaction that can be corrected. My 5 orphan kittens have done that but one will not stop doing it. Why? Because one of his favorite "people" (the gardener) encourage that kind of play. Amazingly, my little Go has learned to differentiate my reaction and the gardener's so he plays quite gently with me and so totally opposite with the gardener.

Great, My worst fears were confirmed, I have a weird cat. I am used to the whole belly rub trap that cats do with the claws and teeth and all. When I adopted Marcie and she flipped onto her back, that is what I expected (teeth, claws, etc...) instead, I have a cat who really likes belly rubs just like a dog. I don't understand...

HI.
My Siamese wanna-be loves to have her belly scratched. He throws himself on to his back, with his legs stretched straight out and expects a good belly-rub from top to bottom. We always oblige.
Isn't it strange how animals have different personalities. My other cat 'Bam' on the other hand hates to be touched on her belly, so we don't.....Karin