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.
Es algo que señaló Robert Provine, como pueden ver aquí, y es la razón por la cual reímos al escuchar esas risas graciosas al principio, y por la que yo reí al descubrir a mis padres riendo, y ese es un enorme efecto de comportamiento contagioso.