You wind this device up and place it over the middle finger of your right hand, with the spike facing away from your palm. When you shake hands with a person, the spike is automatically depressed, allowing the motor to unwind with an unexpected buzzing sound and vibration. It causes both surprise and shock followed, hopefully, by laughter. Another name for this joke is Joy Buzzer. It was a huge success for S.S. Adams, its inventor, in the USA. More details may be found on the web.