Nasty habit

When Josey was younger, he learned that if he was particularly drooly or he'd been crying, he could open and close his mouth, making a weird sound like "Mwlaaaaaa" and he could produce large, nasty, goobery bubbles. He does it quite regularly, and I usually get ticked off and grab a paper towel to wipe inside his mouth so he can't do it anymore. This morning Roanen was playing and talking to himself, and I was shocked and disgusted that he was sitting around, absentmindedly going "Mwlaaaa" and making bubbles. Like it's not enough that one does it??