can someone explain "reaction videos" to me?

[Altruist]

prolly be the first things that take hold in a planet of the apes type scenario where reading expressions and gauging sentiments would prolly have inordinately high survival value, but yeah its just weird now. Half the times Im too concentrated on a slop reel that sometimes pops up that I dont notice the black guy whos taking up half the screen below jfl

high IQ, this guy has it