Some say that cats can be fickle. I suppose that could be said of you humans as well. When we lay on our back, you need to look at more than just the fact that our belly is exposed.
Take this guy, for example. He has such a serious look on his face and really doesn't look like he's quite with it. Perhaps he just woke up. My question to you might be, would you pet his belly given his countenance?
And then there's this one. Now I know my cousin looks soft and furry, but what do you think?
Cats who lay with their belly exposed are often telling you they feel safe and most of the time, they are happy. Getting back to the part I stated earlier; you need to pay attention to the total picture. If their ears are flattened back, I wouldn't touch that with a 10 foot pole unless you like being razor bladed to death! If they're purring, it could be possibly okay, but what's the tail up to?
The fact is, at least with my cousins here, is that you really have no way of know which way this is going to go once you move in for the belly rub. Caution is the word for the day.
Did I mention how soft our bellies are? Who can resist it? Play at your own risk!
Have a purrr-fect pain free day!