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While this method is often discouraged, it will work in a pinch. Even so, if you have a choice of a straight, punch, or wedge cut, opt for those instead of biting the cap off.

Summary:
Understand that biting is imprecise and may result in a poor smoke. Place your teeth in the same manner as with the guillotine cutter. Gently bite a few times while rotating the cigar. After a few bites while rotating the cigar, the cap will be separated and can be removed by hand or mouth.