'Tween the Wars, RAF pilot gets caught short on a flight showing an Army Major around the mountainous Tribal regions of Persia. No alternative but to go where he was.
After the flight the Major thanks him for the tour and says "What was that fluid that leaked back from your cockpit?"
"Err petrol?" hazards the pilot.
"Oh no" said the Major thoughtfully. "It wasn't petrol. I tasted it.. it wasn't petrol...."