Gotta confess, I had to Google this, and then I remembered what it was. I knew the concept but had forgotten the term.

Tee hee. I just saw The Music Man last week and Robert Preston's line from "Ya Got Trouble" always makes me giggle: "Hearin' him tell about horse-race gamblin', not a wholesome trottin' race, no, but a race where they set down right on the horse!" And everybody gasps. :p