I think they rub just because it feels good too. There are some spots/corners in our house that have been rubbed so often I've had to repaint them. And you would think by now that they know they own the whole house, so why rub anymore, but they just keep rubbing. Tubby particularly likes to rub his face on Terry's leg while I'm patting his (Tubby's) butt. He'll alternately bump his head and rub his face on Terry. It's one of our "precious" moments - Tubby likes it, I like it and Terry likes it. Now if we could only get Peanut involved somehow.