Last year McDonald's introduced a new mascot, "Happy," a crazed-looking Happy Meal box, with the intent that it would help sell burgers to humans. A lot of people made fun of Happy, to the extent that it became something of a story, at least briefly, and produced lots and lots of memes.

But why would anyone buy something from a goggle-eyed junk-food golem? The answer is that a lot of us simply don't trust our fellow humans enough.

That's the conclusion of Ann McGill, a marketing expert at the University of Chicago, who just gave a fascinating lecture to the Becker-Friedman Institute. She's a veteran academic who writes papers like "Alignable and Nonalignable Differences in Causal Explanations" and "Is That Car Smiling at Me:  Schema Congruity as a Basis for the Evaluation of Anthropomorphized Products," but sometimes that academese translates into questions like: "do you trust talking dental floss more than an actual human being?"

And really, if you think about it, talking dental floss has probably never let you down, whereas human beings let you down all the damn time.

In McGill's tests, here's what that looks like:

On the left side of the graph, people with low trust in other humans just aren't having it when a person tells you that Max Floss dental floss is great. But the same ad, with the language tweaked so it's Max Floss itself promising that "I am soft on gums but tough on plaque," okay, that's mildly believable.

McGill's theory is that anthropomorphized products fall into a weird gray area of human psychology. It's human enough to cue you to listen—hey, I'm being talked to—but not so human that you wouldn't trust it as far as you could throw it. Trusting, say, a talking margarine box may seem insane, but, well, people are pretty terrible.

McGill's lecture is below. If it doesn't seem convincing, just picture it as delivered by a lectern with a mouth and googly eyes.