One of the most annoying things about Vine was having to wait for a vine to restart so you could turn your phone around and show a friend.
I think it would be really useful if you could touch and hold the screen to pause a video, and Force Touch (iOS) to restart it.
Comedy is about punchlines. If your friend knows the punchline before the setup, the joke loses its impact. I think adding this small feature would add a lot to the user experience.