That isn't true. There are chemicals, though not necessarily "added."

The chemical factory
http://www.plantphysiol.org/cgi/reprint/6/1/183.pdf
Are Cigars Just as Bad as smoking cigarettes?

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A panda walks into a cafe. He orders a sandwich, eats it, then draws a gun and fires two shots in the air.

"Why?" asks the confused waiter, as the panda makes toward the exit. The panda produces a badly punctuated wildlife manual and tosses it over his shoulder.

"I'm a panda," he says at the door. "Look it up."

The waiter turns to the relevant entry and, sure enough, finds an explanation.

"Panda. Large black-and-white bear-like mammal, native to China. Eats, shoots and leaves."

yeah, the chemicals of the tobacco. Meaning it is part of the tobacco.

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Set your destination with your heart, get there with your mind.

"The wisest men follow their own direction." - Euripides

Or at least part of the burning process.

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A panda walks into a cafe. He orders a sandwich, eats it, then draws a gun and fires two shots in the air.

"Why?" asks the confused waiter, as the panda makes toward the exit. The panda produces a badly punctuated wildlife manual and tosses it over his shoulder.

"I'm a panda," he says at the door. "Look it up."

The waiter turns to the relevant entry and, sure enough, finds an explanation.

"Panda. Large black-and-white bear-like mammal, native to China. Eats, shoots and leaves."