As an actor in a provincial repertory company soon after World War II, O'Madden greatly impressed the young Donald Sinden, who was just starting out in the profession. Sinden saw O'Madden underlining various lines of dialogue in his script, and O'Madden explained that he was "marking my laughs". Though several of these lines did not appear to be humorous, he unfailingly got a big laugh from each one at every performance.
