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.
こんなふうに プロヴァイン氏が指摘したこと それから なぜ私たちは 冒頭の可笑しな笑いを聞いて 笑ったのか なぜ私は両親が笑うのを見て 笑ったのか― その理由は この行動が 強い伝染性をもつからです