When referring to why he is going back to see Mr DeVries after being attacked by him , the Doctor says, "because Mr DeVries is a worried man and they often sing a worried song". These are lyrics from Woody Guthrie's song, "It takes a worried man, to sing a worried song". This song was originally done by The Carter family and recorded in 1930.
Part 2 does not begin with a recap of the previous episode, a departure from the series' normal practice.
This episode was watched by 6.6 million viewers on its original transmission.