In article , Roland Perry
writes
There's anecdata about guards making announcements pretending to be on a
plane "Welcome aboard, today we'll be cruising at zero feet above the
rails..."

I've certainly experienced something similar on an HST out of
Paddington. From memory (it was 30 years ago), it was "our cruising
altitude will be five feet".

--
Clive D.W. Feather