Dr. Ulrich: “You mean like some people we both know who expect their checks at the end of every month?” / Teacher: “Dr. Ulrich, you’re impossible! We could still give him reinforcement after he does what we want without using things. Why does it have to be money, tokens, fruitloops, and things like that? Why can’t we just use a smile or something like that? Why can’t that work?”
Source: wiktionary