what does it mean when

[Mitch]

Imagine you have had your smoke lit for a minute or 2, the burn looks even, but somebody has taken a needle or something and scraped out some tobacco between the bulk of the filler and the wrapper, usually in more than just a small spot, which why its hard to correct by touching up. Lightly squeezing the cigar pre-light (which I always do) isn't overly mushy and no soft/hard spots.

I think I'm sticking with my original guess that it's where the tobacco folds. Looks a bit like tinly worm holes in the ash that were not there when you lit the cigar? Take a close look at the patern of tobacco in the foot next time and see if this may be it.