3 looked at Benjamin. It did know what a promise was, the children it played with talked about them all the time, but as far as the puppet knew a promise was a guarantee, something that had to be done. How could Benjamin promise that he'd find a man that 3 had been searching for for over two hundred years? Had 3's idea of a promise been a "lie" as well. 3 had difficulty wrapping it's head around the idea that someone could tell falsehoods, and it suddenly felt itself questioning everything it had even been told.
It was silent for several moments processing this before it decided to deal with the problem of reconciling all it's knowledge later, and dealing with the problems now. 3 was not looking forward to the task of sorting truth from lies. It now realized that much of the things it had been told in it's memories conflicted, and discovering which was correct was going to be an arduous task indeed.
Putting that off, 3 looked into Benjamin's eyes, and asked him, "You promise that we'll find him?" It stood for a moment longer, thinking. "A promise is a guarantee that you'll make it happen, right? This isn't one of those lie things you were talking about?"