In this Moment of Science Don and Yael discuss more evidence of the dangers of talking on cell phones--hands-free or not--while driving. D: It's time for a new feature on our show, called I Got the Data. This is where I say something that a smart-alec at a party would no doubt disagree with, and then I triumph by having data to back it up. Yael will play the smart-alec. Ready?

Y: Ready.

D: Nice party, huh? I love these chips.

Y: Mmm-hmm.

D: You know, on the way over here I saw this guy talking on a cell phone while driving. That's got to be dangerous.

Y: No it isn't. Only idiots can't drive and talk at the same time.

D: But your hands are off the wheel.

Y: I got one of those no-hands cell phones you can mount in a car. Don't believe what anybody says. They're completely safe.

D: Unfortunately for you, smart-alec, I Got the Data.

Y: You what?

D: A study done by a psychologist and an engineer at the University of Rhode Island had volunteers wear eye-tracking devices while they drove. The researchers found that a driver's eyes move around a lot--we scan the road, check our speedometers, and stay alert for surprises. When talking on a cell phone at the same time, though, eye motions fell to almost zero--the subjects simply stared at the bumper ahead of them.

Y: Yeah?

D: The issue seems to be not talking on the phone per se but concentrating on a second task, such as making a decision with the person on the other end of the line. When we do that, we take our mental energy away from driving. And that's dangerous!

Y: I knew that.

D: Mmm-hmm.