Detecting a Coming Betrayal

"Researchers use transcripts from online Diplomacy games to identify signs of imminent betrayal":

One of the key signals of a coming betrayal, oddly enough, is that betrayers are especially positive compared to other players before they turn on their allies, potentially a sign "the betrayer [is] overcompensating for his forthcoming actions," the team explains. Future victims, meanwhile, are more likely to talk about pending plans and are also somewhat less polite in their messages to others.

Related excellent article on the game Diplomacy: "The Board Game of the Alpha Nerds".