A reference to Agatha Christie's 1939 novel in which ten characters are killed off one by one. The book, later retitled And Then There Were None, drew its original title from a nursery rhyme which in turn derives from an 1868 song called "Ten Little Injuns":
Ten little Injuns standin' in a line,
One toddled home and then there were nine;
Nine little Injuns swingin' on a gate,
One tumbled off and then there were eight...
and so on...
Listen on Spotify: Ten Little Indians performed by Harry Nilsson