The Doctor occasionally touched, tapped, or rubbed his cat brooch for good luck just before doing something particularly risky. (TV: The Twin Dilemma, Attack of the Cybermen, Vengeance on Varos, PROSE: Retribution, Time Wake) When Peri Brown was put on trial for a murder she didn't commit, the Doctor proved her innocence in part by using his cat brooch to collect a blood sample from the real killer. (COMIC: The Forgotten) One of the cat brooches appeared to change its expression to match the Doctor's mood. (WC: Real Time)