Katherine Heigl has been battling a cigarette addiction for six years, but finally has found a solution to her problem: a "smoke stick."

The "smoke stick" is actually a so-called "e-cigarette" -- a battery-powered device that lets you inhale nicotine while puffing out a cloud of (supposedly) harmless water vapor.

On 'Late Show' (weeknights, 11:35PM ET on CBS), Heigl demonstrated the smoke stick for David Letterman, and Dave was so impressed, he tried the "e-cigarette" out for himself. And he liked it!