In professor T. Mills Kelly's class, students act out clever public hoaxes. But while Wikipedians are easily fooled, Redditors exposed the latest jape—Do you think my 'Uncle' Joe was just weird or possibly a serial killer?— instantly. Yoni Appelbaum at The Atlantic unravels what happened.

Although most communities treat their members with gentle regard, Reddit prides itself on winnowing the wheat from the chaff. It relies on the collective judgment of its members, who click on arrows next to contributions, elevating insightful or interesting content, and demoting less worthy contributions. Even Mills says he was impressed by the way in which redditors "marshaled their collective bits of expert knowledge to arrive at a conclusion that was largely correct." It's tough to con Reddit.

This isn't quite true. Reddit is vulnerable to cons: just not this kind of con. Academic hoaxes are the sort of thing Reddit can see through easily. Superficially weighty evidence doesn't trick an audience exquisitely tuned to the forensic texture of information; the site's machinery heaps attention on anything interesting; and the social milieu makes it hard for would-be hoaxers to avoid adopting a pattern of behavior ("karma whore") that threatens their credibility from the outset.

On the other hand, Wikipedia is easy to deceive because it's easy to accumulate low-profile, cross-referenced edits, and the site has a rigid, exclusionary culture that is easy to exploit once it is understood.

However, those iffy props really didn't help! To quote Redditor TruculentTravis: "The papers look falsely aged. I can tell from the burnt edges, and from having seen many falsely aged papers in my time."