Naccirema

Chocolate bars have a circus trick, an "Oh, my" moment: They're solid when you unwrap them. They make a satisfying snap when you break off a piece. But then, when you put that piece into your mouth, when it's resting on your tongue, it turns liquid. A chocolate bar, Miodownik says, jumps states so quickly, it is, in effect, a paradox: "a solid drink ... made possible by engineering."

The secret ingredient is cocoa butter, stored in the form of large molecules called triglycerides that come with three (thus the "tri") prongs. Inside the chocolate these fat molecules are jammed together, but sensitive to temperature. They can sit very loosely, like this "Now, in your mouth," Mark writes, "they experience higher temperatures for the first time. This is the moment they have been created for. It is their first and last performance. As they warm up and reach the threshold of [your body temperature, 98.6 degrees F], they start to melt. This frees them to move around as a liquid."

Once it starts to flow, says Miodownik, chocolate is soothing and comforting, but it is also exciting and — not to put too fine a point on it — seems to satisfy more than a physical hunger."

Is Chocolate Better Than Kissing?

People (it's no secret) really like chocolate. The signs are everywhere. Chocolate billionaires proliferate on the Forbes list of the richest people in the world (Michele Ferrero of Italy, who makes Nutella, is worth $27 billion; Forrest Mars, Jacqueline Mars and John Mars who make Milky Ways, Snickers and M&Ms, are collectively worth about $60 billion).

Then there's the science. In 2007, David Lewis, a psychologist now at Mindlab International in Britain, recruited a small number of couples, all in their 20s, attached electrodes to their scalps, monitored their hearts and asked them to suck on pieces of dark chocolate. Which they did. Then he compared the effect on their bodies — kissing versus tasting chocolate. It wasn't a big study (six couples) and it