Synopsis:
The Huxtable kids throw a lunch party for Cliff's 50th birthday. They get him a keychain that beeps when you clap, but Cliff is the only who can't get it to work. Cliff invites some friends over that evening for a party, and Clair is upset to see that he invited Mark, someone who was once married to one of her good friends but cheated on her. Mark and Clair have a long talk, and Mark begs for Clair's forgiveness.