I did a similar trick out on the line, doing combat preps during a 'Mick'. A brand new OC Eng was wandering about outside as we were about to do a special weapon load and he'd never seen it done before. Attracted by a buzzing noise from just behind the stbd gear he went to take a look. My catcher behind the port leg reported a blank drop. There was a cough from the other side. One Wing Commander covered from head to toe in fairy dust. Merry Xmas Sir!