For something I can’t tolerate or must be stopped, I’ll do this:
1. tell the kid calmly and seriouly what he did is wrong and I am unhappy, no more or I’d hit his mouth.
2. if he did again, stare at the kid seriouly and repeat the warning calmly.
3. if he did again, tell the kid he did the same wrong thing and remind him the warning and I am going to hit his mouth. I did it mildly but the kid must feel the pain.
For me, it works.
No problem, he is trying to control the movements of his mouth.
During shower time, let him do as many time as he wants. My son stopped to do so in 7-10 days after he found it was not interesting.