A penknife was a small knife the Fifth Doctor regularly carried but Turlough did not. Nyssa, commenting on the surface of Samur, believed that Turlough should have carried one since he was "a boy". Elsewhere on the planet, Tegan thought that the Doctor's possession of a penknife confirmed her suspicions that he had been a Boy Scout. (AUDIO: Heroes of Sontar)
Barbara Wright asked if anyone had a penknife to use for cutting apart her cardigan. (TV: "The Dimensions of Time")