the most likely to fire if a mag is live
It was hammered into me in basic training that a hot aircraft piston engine can fire (as opposed to "start") if a cylinder goes over compression
regardless of whether one or both magnetos is(are) live. Therefore pulling on a hot prop, or even turning one for any reason apart from starting using the proper technique, was an absolute no-no, dead magnetos notwithstanding.
I always assumed that this would simply be the result of compressing the hot gas until ignition occurs (a degree or two after the spark would have occurred?) because the gas is heated in the hot cylinder to begin with, which sounds plausible to me.