Think you're good at multitasking? Most of us believe we can do several things at once—like talking on the cell phone while we're driving. But maybe we're not as good at juggling as we think.

To see how well people pay attention while they're on the phone, researchers sent in the clowns—literally. They had a clown on a unicycle pedal around a college campus for an hour.

Then, pedestrians were stopped and asked if they'd noticed anything unusual.

Most people who were listening to music or walking with a friend did recall seeing the clown.

But only 8 percent of people who'd been on their cell phone at the time could remember seeing him. And even when the researchers specifically asked, "Did you see the unicycling clown?" only a quarter of cell phone talkers could remember.

Now to miss something like that you've got to be pretty distracted. People who were gabbing away also walked more slowly and erratically than those who were phone-free.

If talking on a cell phone makes it that hard to pay attention when you're walking, imagine what it's doing when you're behind the wheel. That's why it's a good idea to stay off the phone, so you can keep your mind on the road.