Vacuuming a carpet too much can damage it.

False. This myth, perpetuated no doubt by the couch potatoes of the world, horrifies cleaning experts. “It is absolutely, positively untrue,” says Jeff Campbell, author of Speed Cleaning (Dell, $11, www.amazon.com). The dirt that settles in the fibers is the real danger, as it can weaken them over time. Vacuuming daily with a rotary brush, however, could cause fibers to fray unless you raise the brush to a high setting, says Jeffrey Gross of the Association of Specialists in Cleaning and Restoration. Rotary brushes should also never be used on Oriental or antique rugs, says Gross, because they can cause excessive wear and leave permanent marks.

Using the phone during a lightning storm can be dangerous.

True. Both the Electrical Safety Foundation International and the National Oceanic and Atmospheric Administration (NOAA) advise against handling corded phones during thunderstorms: Lightning could send a charge from the pole outside through the wire feeding into the phone and “right into your head,” says John Jensenius, a lightning expert at NOAA. (Cordless phones out of the cradle and unplugged cell phones aren’t a problem, he says, “since there’s no physical connection with outside wiring.”) However, “the probability is low,” says Richard Berg, a physics professor at the University of Maryland, in College Park. For one thing, he says, phone lines aren’t designed to carry a current as strong as a lightning bolt, so they’d probably melt before it got into your home. Jensenius agrees the chances are “relatively low” but adds, “if you are struck, you could be injured or killed. It happens every year” (an average of 8.7 times a year, according to NOAA data). So, granted, you’re probably going to get away with it, but unless there’s an emergency, why tempt fate?

Leaving grass clippings on the lawn after mowing is harmful.

False. In fact, this process, called grass cycling, allows the nutrients to return to the soil, says turfgrass science professor Trey Rogers. However, if you’ve neglected the lawn for months, then suddenly have an Edward Scissorhands moment, you could have too much of a good thing. “If the grass is really tall and you leave large clumps,” says Rogers, “they won’t work their way down to the ground, and there’s a good chance they’ll smother the turf.”