They say that laughter is contagious but that's ridiculous.
I want to know what they were laughing at.
perhaps the person who was recording them was in the nude and had a very small wotsit.
I reckon some of them are actors, or maybe even all of them. Some of them are only managing a stiff smile. The British are too self contained to act like that. Yawning is contagious too (no joke).