Know how to use "fewer" and "less"? Find out.
also heeltap, 1680s, "one of the bits of leather that are stacked up to make a shoe heel" (see heel (n.1)); meaning "bit of liquor left in a glass or bottle" first recorded 1780s; the exact connection is uncertain unless it be "the last or final part."
A few drops of liquor left in a glass: drink three martinis, absolutely no heeltaps
[1780+; origin uncertain; a heeltap glass was one without a flat base, so that it could not be set down until entirely empty (such was presumably also a tumbler), and probably so called because the narrow bottom resembled the narrow tap of a shoe heel]