In reality, however, there’s much in the way of conversation and other communication that could contain hints of what’s to come, the researchers argue. To probe what such information could yield, they needed a large body of communications to analyze. For that, the team turned to the classic game Diplomacy—in particular, to transcripts of 249 online games, containing a total of around 145,000 individual communications between players. The data also included information on which players explicitly supported others, as well as signs of hostility, such as invasions or support for a player’s enemies.

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.

How those variables change over time matters, too. In the moments before they’re betrayed, victims start talking more and more about future plans and become increasingly polite. Conversely, betrayers suddenly express positive sentiments—for example, “I will still be thrilled if it turns out you win this war”—and suddenly less polite, despite having been the nicer one for much of the game.