Some celebrities have been seen "smoking" electronic cigarettes, also known as "e-cigs." E-cigs are electric inhalers that vaporize diluted nicotine and propylene glycol solution directly into the bloodstream (as opposed to the lungs). They're advertised as safer and healthier than the tobacco variety (though the jury's still out). But really, who cares about science? Stars like Robert Pattinson, Katherine Heigl and and Zac Efron might be onboard. What else do you need to know?