Q. Stand on your head and the world looks upside down. What if things always looked this way?

A. To find out, psychologist George Stratton (1896) designed inverting glasses, then wore them for eight days. At first he stumbled around, had difficulty eating, got nauseous and grew understandably depressed.But by the eighth day he could walk comfortably and reach out and grasp objects. Then he ended the experiment and readjusted just fine.

Other more recent studies have found wearers able to ride a motorcycle, ski the Alps and pilot an airplane, reports Hope College psychologist David G. Myers. It's not that subjects stopped seeing the world as wrongside up, but they eventually learned to coordinate their movements within this very novel context.

Q. Do blind people see in their dreams?

A. They do if they once had sight, though the dream images fade over time. People born blind have no pictures but dream vividly in the other senses.

Q. Try an experiment: Watch a funny video while holding a pen between your teeth, then watch it while holding the pen with your lips. Can you feel a difference?

A. Subjects in an actual study rated movies funnier when the pen was between their teeth, which forced their mouth open into the expression of a smile (unbeknownst to them). With pen between lips (simulating a frown), watchers found less to laugh about.

This "facial feedback," say researchers, is the reason putting on a happy face can actually make you feel happy.

Q. Stick one hand into a pot of water and it seems warm. Stick the other hand in and it seems cold. How is this possible?

A. Assemble three containers of water - one hot, one cold, and one lukewarm. Submerge a hand into the hot water and the other into the cold, then keep them there for several minutes. Now place both hands into the lukewarm water. One will feel hot and the other cold, even though they're both in the same water!

Q. What happens when two powerful locomotives are set to racing open throttle toward each other on the same track? Showman P.T. Barnum never tried this, but a man named William Crush of the Katy Railroad did, in Waco, Texas, in 1896, before 30,000 spectators.

A. As recounted by David Halliday et al. in "Fundamentals of Physics," the pair of engineer-less 270,000-pound locomotives sped at 90 mph each, totaling 180 mph approach velocity. They collided with a fury equivalent to 100 pounds of TNT, calculations later showed. Too bad the figuring wasn't done beforehand: shrapnel and debris flew everywhere, killing several "ringside-seated" onlookers.

Q. In 1816, when Dr. R.T.H. Laennec was examining a young, obese woman with symptoms of heart disease, he balked at feeling her chest with his hand or placing an ear there (the standard methods of the day), believing these to be "indelicate and impracticable" under the circumstances. What device did he invent on the spot?

A. He rolled up sheets of paper into a tube, put one end to the woman's chest above her heart and listened at the other, the precursor of the stethoscope, say John R. Cameron et al. in "Physics of the Body."

Q. Millionaires are getting to be a dime a dozen. But there still aren't many billionaires. What's the difference between the two?

A. You can take this to the bank: If you went on a feverish spending spree amounting to a dollar every second, 24 hours a day ($86,400 daily), it would take you only 11 1/2 days to blow a million but nearly 32 years to kiss a billion goodbye.