I searched the archives and found this:
"Boogers and dirt...
Marty used to eat his boogers in front of the family, when he was little. I teased him out of it by offering to ask a friend of ours who worked at the zoo to save him some monkey boogers, or elephant boogers. I grossed him out gently, to help him see that he was grossing us out.
I told him he could do it in his own room, but not where other people were.
Sticking fingers in ANY holes in bodies, I used to say, was for privacy. Nobody wanted to see the insides of them, or what comes out of them, I'd tell them. So it wasn't a specific rule, it was a principle about bodily lumps and fluids, and about exploring our own orifices and parts."
Bodily lumps and fluids and exploring orifices and parts hits it right on the nose. I guess I've hesitated to use humor or gentle teasing for fear of teasing a little too hard, but maybe that would be good to switch it up and get out of this "here goes mom again" broken record thing.