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.
wenn wir wie zu Beginn Lachen hören. Ich lachte, als ich meine Eltern lachen sah, weil es unglaublich ansteckend ist. Man kann sich von jedem anstecken lassen.