Belly Rub?

Sadie is so spoiled, and I think she knows that she can pretty much get whatever she wants. She has this new habit, and I don't know where she picked it up. If me or Lee are sitting down and one of our legs are crossed, so one of our foots is in the air she will come over to it so we can pet her with out feet. You may be saying, ya that's normal for dogs to do. But wait, there's more! When she comes over, if we don't start petting her right away she will lift her back leg, and extend it out so we can reach her belly. The first couple of times she did it, we thought it was a fluke, but its now a everyday occurrence.