english: Something that Robert Provine has pointed out, as you can see here, and the reason why we were laughing when we heard those funny laughs at the start, and why I was laughing when I found my parents laughing, is that it's an enormously behaviorally contagious effect.
non_english: Wat Robert Provine heeft opgemerkt, zoals je hier ziet, en waarom wij in het begin lachten toen we gelach hoorden en waarom ik lachte toen mijn ouders lachten... is dat lachen heel aanstekelijk is.