Singer Marni Nixon, who famously dubbed the singing voice for actresses in many musical films, appears as a contestant on "To Tell the Truth" in this segment from a 1964 episode with host Bud Collyer and panelists Tom Poston, Peggy Cass, Orson Bean, and Kitty Carlisle.

Her reputation as a famous "dubber" was well established by this time, though her face was not well known, so she could plausibly appear on this show and not be recognized by any of the panelists. Interestingly, though it was well known and widely reported that she had dubbed Audrey Hepburn's singing voice in "My Fair Lady", that still wasn't being officially acknowledged at this time. So Marni (and the impostors) had to deflect questions about that movie.