Ding (or Take That Back)

One at a time, participant begin improvising a monologue about anything they like. As they go along, the leader will ding a bell, or say "ding" or "beep" or make some previously specified noise at various points and the person who is improvising must got back and change their most recent statement. For example: " When I was little, I loved swimming and-" ding "I absolutely hated swimming . . . " and then they continue on with their story.