Those of you of a certain age will remember that some local trains had separate compartments seating 6 a side, each of which were accessed individually with no access to any other part of the train. Turned out the train we were on was not a semi-fast but stopped at all stations, realised just in time to avoid two old dears getting an eyeful. They sat there the rest of the journey looking at each other, then at us, then smiling.