The Trio steal $1000 from a baby - but they don't care, because babies only understand the "emotional economy", not the financial one. There is a giant "psychological marketplace" that parallels the monetary one, in which people participate through their relationships with each other. They instinctively trade psychological commodities - but sometimes these instincts go astray and the underlying workings of the economy must be examined.
The idea behind this episode is actually rather easy to grasp - that the economics of trading in a marketplace also apply to human relationships, where you have a kind of psychological energy being traded instead of money. People feel bad when they get a bad bargain and happy when they get good ones. A useful metaphor indeed!