do you re-use an unconsumed cigarette?

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when you suddenly have to leave your cigarette and you put out its fire and when you get back, you realized it was used only for one puff. do you have to light it again and consume the rest of the cigarette? do you think this is a good practice? well, considering smoking is not at all a good habit. but will you think it's a waist to throw a cigarette like that? someone told me before its char (coal) is actually dangerous (more risky) as it emits more dangerous chemical. that this re-used cigarette is giving more toxins causing cancer (of lungs).