The robots were programed to think that two of them had been given a “dumbing pill” that would make them unable to speak (actually just a button that silenced them). However, they didn't know exactly which two of them had been silenced. When the robots were asked to answer which two had been given the pill, all of them tried to respond: “I don’t know.” Since only one was actually able to utter the words, it heard its own voice and recognized it wasn't among the two who had been silenced. That robot then responded: “Sorry, I know now. I was able to prove that I was not given a dumbing pill.”