Sam Anderson via NYTimes.com

The most striking thing about reaction videos, if you watch a string of them, is their sameness. There are little stylistic differences — one guy will shriek and jump out of his chair; another will just sit there open-mouthed — but everyone basically has the same responses at the same moments. The great lesson of the genre is that we are physically different — our couches, beds, hairstyles — but spiritually uniform. A grandmother sitting in front of a ferret cage is the same as two college girls in a dorm room. This is part of the appeal of reaction videos: they allow us to experience, at a time of increasing cultural difference, the comforting universality of human nature. It’s no accident that all of this started on YouTube in 2007 — at a moment when, and in a place where, human experience was beginning very visibly to splinter. Watching thousands of people react identically to “2 Girls 1 Cup” (“Come on!” they invariably shout, and “Why!?”) feels like a comforting restoration of order and unity. Which means that the most disgusting and offensive video ever to go viral was ultimately, oddly, a force of togetherness.

Reaction videos are designed to capture, above all, surprise — that moment when the world breaks, when it violates or exceeds its basic duties and forces someone to undergo some kind of dramatic shift. This is another source of the genre’s appeal: in a culture defined by knowingness and ironic distance, genuine surprise is increasingly rare — a spiritual luxury that brings us close to something ancient. Watching a reaction video is a way of vicariously recapturing primary experience.