Heard a tale once of a commercial flight just about to cross the fence and touch down. The Capt looked across to the FO and by the sad look on the FO's face reckoned the FO was having a very bad day. Thinking to make the FO happier the Capt said "cheer up" at which point the FO reached forward and retracted the undercarriage ! Of course I don't believe a word of it :-)