My 6 year old asked me that question tonight and I had no clue! I was holding my cat on my lap and trying to gently rub her belly--she doesn't like it!--to see if I could feel anything in there!
My Lexus didn't like belly rubs either until she was so fat she looked like she had swallowed a grapefruit! Then, she would only let my husband rub her belly by stretching out long and curved outwards ... she is such a tart.
Sheba has 8 as well and Gaye my baby did the same thing, no one else can rub but me and she pulls out on the side to make sure I rub it all! which is unusual because she AINT the rubbin' type but hey mama's enjoying it Anyone else and she is ready to bite!