I hesitate to intrude into the company of so many experts, but when I was doing my Primary School on the Arnold Scheme in '41 with the Stearman, I was taught that the Snap Roll was simply one turn of a horizontal spin, the preliminary stall induced by a sudden increase of the AoA when flying slightly above normal stall speed. They taught a half-Snap roll, too, which they called a "Snap Vertical Reverse".
The idea here was that, in a tight left turn, say, you executed a SVR to the right, which left you in a tight right turn, to the sudden dicomfiture of the chap who had been tailchasing you.
Even as a clueless LAC (masquerading as an Aviation Cadet in the USAAC), it struck me that a Tiger Moth (which I had never flown) would not survive this treatment for long.
Curiously, many years later ('50), I was taught that the best way to spin the Meteor 7 was to snap-roll it into the spin. The first few seconds after the snap were a true "out of the body" experience. Some time after that, intentional spins in the Meteor were prohibited (and a good thing, too).
Danny42C.