"The Worm of the Still," referring to the coil on a still. I had to read the passage over several times before I "got" it myself, because I had read it as a literal reptile.
Maybe this one was too hard. Keep in mind that McGuffey Readers were public school textbooks, so I suppose this would qualify as an olde-fashioned "health" class warning of the dangers of drink. Ah, well. It seems a weeee mite overexaggerated, but least they didn't try to put a condom on a banana. :)