The difference between extending and flexing your arm at the elbow is when you flex your arm at the elbow it tightens,when you extend your arm its takes longer to reach the potential of the flexing part.
I would influence my friend to stop by telling them that it isn’t good for them, and some facts about tobacco, to hopefully inform him about why he should try to quit. I think that it’s important for a teen to never try tobacco because it can damage their lungs, and change the way they think, impacting their brain and potentially their muscles as well.