Fast-food menus are among the most rigorously tested products of our consumer culture. Because the decision of what to order for lunch isn't that important in the grand scheme of things, we don't spend much time or thought on it. Instead, we rely on subtle cues in . Say your friend mentioned having a barbecue sandwich yesterday. The odds are, you're more likely to try a McRib sandwich today (assuming you like barbecue, and the friend). Memories are short, so the most powerful source of cues is the menu. Chains know that and spend a lot of effort on their menus. In many cases, menus and prices are intended to nudge consumers into ordering more than they might have otherwise.

• The Starbucks menu uses the "rule of three." The menu offers three sizes of coffees, given the enigmatic names of Tall, Grande, and Venti. (They're 12, 16, and 20 ounces respectively; 24 ounces for cold Venti drinks, to allow for ice.) Since Starbucks newbies won't know what they're getting, they tend to order the middle choice, Grande. In the psychology literature, this is known as "extremeness aversion" — people instinctively favor a middle choice, figuring it's safer. Guess what? You've just ordered two cups of expensive coffee. The Grande's sixteen ounces is two regular cups. Here's a secret: Manys Starbucks will serve you eight ounces of coffee, but you have to ask for a "Short" coffee (which isn't listed on the menu). You do have to remember that password "Short," though: Company policy says that a customer who asks for a "small" coffee is to be given a "Tall" one.

• Anyone who doubts the power of prices ending in 9 should check out a fast-food menu. The menu above, at a Los Angeles Pollo Loco outlet, has 75 prices, and all but one end in the digit "9."

• The exception: a deal offering 10 buffalo wings for $5. Quick: How much is that per wing? It takes most of us a moment to do the math. And that's the point: not many people bother, not with kids screaming in the back seat. But "10 wings for $5" sounds like a better deal than "50 cents a wing."

• The most common trick of fast-food menus is the "combo meal." As everyone understands, the combo meal offers an incentive to order something extra. The burger plus fries plus soda combination costs just pennies more than burger plus soda à la carte. You might as well get the fries — you're practically throwing away money if you don't order them. For most consumers, this train of thought is irresistible.

There's another reason fast-food places offer combo meals. They foster confusion. It's hard to be sure how much the burger costs, and how much the drink costs, and whether it's too much. So consumers are a bit less price-sensitive with combos. Of course, eventually repeat customers become familiar with the prices of their favorite combos. For this reason, fast-food menus are an ever-changing caloric kaleidoscope. New entrees are offered, and old ones change or vanish. Combos can be super-sized. Do you want curly fries? You can't buy exactly the same thing you did last time (neither can you compare prices, exactly).

• Critics have blasted the nutritional value of fast food, causing both the industry and government to take action. Since 2008 New York City has required fast-food places to post calories—in large fonts—on menus. This may or may not have promoted healthier eating. It probably hasn't hurt chain profits, though. The reason is that consumers now have two sets of numbers to juggle: calories and dollars. As many experiments have shown, the human mind has a finite capacity to deal with numerical information. By encouraging diners to pay more to calories, the new menus prompt them to pay less attention to prices. That gives chains scope to charge a little more. (Not only that, the salads are among the most expensive things on the McDonald's menu, anyway.)

SEE ALSO

Poundstone, William. "Menu Mind Games." New York, December 14, 2009.

Poundstone, William. "Menu Psych." YouTube, 2009.