Harold McGee plays with his food and encourages everybody else to do the same.

Most cooks look in the cupboard and wonder what to cook; McGee wonders why it cooks the way it does. He doesn't take much for granted, and he's willing to set up all kinds of experiments to figure out why.And readers of his book, "The Curious Cook" (North Point Press, $19.95), are better off as a result. He figures out whether searing meat really seals in the juices, whether it matters if you cut or tear lettuce for salads, why the oil collects on the inside of his glasses when he fries food, and how to make mayonnaise without fear of salmonella. (Answers to come.)

McGee, who also wrote the respected "On Food and Cooking," writes that his new book began when he "came to realize that the professionals have overlooked much of what goes on in our kitchens. Their research generally centers on questions of commercial importance."

Of more interest to McGee were such matters as how saturated fats could affect the heart, why some foods are considered valuable in the fight against cancer, and why it is people generally seem to like cooked foods better than raw.

Most of his experiments are done from beginning to end in his kitchen, and readers so inclined could replicate many with easily obtained equipment. McGee explains simply and clearly what he's asking and how he searches for the answers.

Some of his discussions might appeal only to relatively serious cooks. For example, those who don't make beurre blancs (butter sauces) or who are avoiding them because of their high fat content, may not care how it is they emulsify without the addition of eggs.

But even if you don't eat Jerusalem artichokes and couldn't care how to lessen their potential to cause flatulence, McGee's blend of science and history is fun to read.

And now some answers:

- No, searing meat does not seal in juices, McGee found after repeated searings and weighings of various pieces of meat. Instead, juiciness is determined by how well done the meat is.

However, McGee doesn't recommend tossing out the method altogether: "A very hot pan will begin cooking the meat right away and will intensify the meat's flavor by browning the juices that flow from it," he writes.

- The oil collects on the inside of glasses for a logical reason: Cooks generally look down on the frying pan; oil is carried up into the air by the heat, and when it falls, it falls on the surface that is facing up.

- Of the lettuce, McGee writes, "I could detect no difference between the cut leaves and the torn ones." Even in a vinaigrette, the cut and torn leaves darkened or wilted at the same rate. What does matter, he said, is to dress the lettuce at the last possible moment.

- McGee devised a recipe for mayonnaise and other yolk-based sauces made by boiling the lemon juice or vinegar and yolks in a microwave oven to kill the bacteria before adding the oil.