There’s an extremely cool test over at the BBC’s web site, where they play you video clips of 20 people smiling and you try to guess which ones are fake. Apparently, most people are bad at this, possibly because society would pretty much implode if we were knew just how miserable most of us are most of the time. I got only 13 out of 20 right.

In case you’re wondering how to spot a fake smile, the BBC has some suggestions — based on analyzing the physiology of smiles:

Fake smiles can be performed at will, because the brain signals that create them come from the conscious part of the brain and prompt the zygomaticus major muscles in the cheeks to contract. These are the muscles that pull the corners of the mouth outwards.

Genuine smiles, on the other hand, are generated by the unconscious brain, so are automatic. When people feel pleasure, signals pass through the part of the brain that processes emotion. As well as making the mouth muscles move, the muscles that raise the cheeks – the orbicularis oculi and the pars orbitalis – also contract, making the eyes crease up, and the eyebrows dip slightly.

Lines around the eyes do sometimes appear in intense fake smiles, and the cheeks may bunch up, making it look as if the eyes are contracting and the smile is genuine. But there are a few key signs that distinguish these smiles from real ones. For example, when a smile is genuine, the eye cover fold - the fleshy part of the eye between the eyebrow and the eyelid - moves downwards and the end of the eyebrows dip slightly.

This reminds me of my nearby McDonald’s, which I frequent way too often for my own good. About two months ago some manager put up a sign saying “If we don’t smile while we serve you, tell us and you’ll get a free hash browns or small fries with your next meal!” Beneath that it reads something even more sick, like “Go ahead — we love it when you catch us!” The first time I saw it I thought, christ, that can’t be real; that has to be some particularly subtle form of culture jamming. But it’s real, and were I to actually take the managers up on their offer, I could basically feed myself entirely for free off the sadness of McDonald’s employees, because in the last month I swear to god I haven’t seen a single cashier flash a smile once. Not even, dare I say, a fake one.