After a White House state dinner, President Reagan asked President Gorbachev to play some Russian folk melodies on the piano.
Mr Gorbachev sat down at the oiano, and noticed a red button at the side of the keyboard. Curiosity got the better of him, and he pushed it.
Immediately a bucket of water dropped from the chandelier, drenching the president. He smiled good naturedly as Reagan and his aides guffawed with laughter.
Some months later, President Reagan visited Moscow. After a Kremlin dinner, President Gorbachev asked that Mr Reagan play some cowboy ballads on the piano.
Mr Reagan sat down, and he too noticed a red button by the keyboard. 'Fair is fair,' he thought to himself, and pushed the button.
Nothing happened. One of Gorbachev's aides began to snicker. Soon the Russians were all laughing uproareously, punching each other's shoulders.
Reagan was perplexed. 'Please,' he implored Mr Gorbachev through an interpreter, 'tell me the joke. No water has fallen, yet you are laughing. Please explain your unique Russian humour, so that I may share it with the people of the United States.'
Gorbachev at last regained his composure. 'What United States?' he smiled.