Others who know that better than me and commented but... First time I read that, as a kid, here was I plugging my headphones into the input jack of my parents'

Others who know that better than me and commented but... First time I read that, as a kid, here was I plugging my headphones into the input jack of my parents' soundsystem and, sure enough, it worked as mic (although at as super ultra low volume but I clearly remember it worked).