Laughing!
 

I was on a set, when a little kid actor refused to laugh. It was a last shot of the movie. Everyone wanted to go to a local tavern. We tried everything to make him laugh. Two actresses were told to make funny faces; the kid would just sit there with a serious face. The woman-director then stops everything, leaves, finally comes back and keeps on looking at the kid with a serious face; the kid does the same; some serious tension in the air. Then the woaman opens her mouth from which comes out an egg. The kid bursts in laugher. It's a wrap.

Good job. You have to be inventive.