A friend of my fathers is a university lecturer.
He was set to talk to first year engineering students, mainly 18 year olds and as rough as Old Nick, the talk was on ethics and part of the discussion was to watch a short film on the subject using a TV on a mobile stand with a DVD player. He wheeled in the 60inch screen into the room, gave a short talk, set the film going and then went for a cup of tea.
He returned 10 minutes later, no TV, no player and no stand.
All the students denied ever having seen a TV or the stand, they were very convincing, he thought he was going nuts.
Knowing that there was not much he could do or say he carried on with the talk.
At the end of the morning one boy left the room and returned with the TV.
'As it was a talk on ethics we thought we would put it to the test'.
He saw the joke, eventually.