If you think about it... cigars are full of flavor, oils, and moisture. AS you smoke and the cigar gets smaller all of these goodies including the nicotine begin to accumulate in what is left of the cigar. Some is washed away as smoke but a lot of it accumulates. As you keep smoking yu work through that accumulation and viola, the spins. The black stuff is a mixture of resins, tobacco juice, and tar. DO a small second cut. All gone. I like to purge which helps but if you get a bitter taste, just remove it.