Three 1 to Three 2: She observed with quiet interest the difficulty Jules had of drawing a junior-size sheath over an organ that looked abnormally stout and at full erection had a head turned somewhat askew as if wary of recieving a backhand slap at the <decisive moment>.
Looks like Nabokov deleted the last two words in this sentence in order to avoid a reference to the English tranlastion of Henry Cartier-Bresson's Images à la Sauvette (The Decisive Moment). Has anyone ever come up with the same explanation?