"Pit of Peril" features only five of the regular puppet cast (Jeff, Scott, Virgil and John Tracy, and Brains) – the lowest number of any "Thunderbirds" episode, and is the only episode of the series to have no female characters.The puppets that play Colonel Sweeney and Frank first appeared as Captain Hanson and the unnamed "Fireflash" co-pilot in "Trapped in the Sky".