A pasttime where two squaddies can partake in other games, such as Pontoon, Snap, Gurning, etc. where the doris involved offers her back as the gaming table. The squaddies thank the obliging bint by giving her a measure of longitudinal stability using the appropriate inserts.
After considerable experience it is recommended that one of the blokes has a signal whistle within easy reach.
Once proceedings have been under way for a while he shows it to his oppo who should silently acknowledge that the time is right.
On receipt of the signal he should get closer to the head of the 'table' and blow the whistle as hard as possible.
Both squads then withdraw & run around the room like shouting, "Half time ! Change ends !"
See also spit-roasted