- The Doctor once claimed that he was standing at Wellington's side in the Battle of Waterloo, but later claimed that he stood with Napoleon.
- The Doctor mentions Frontios, Refusis and Balanystra as worlds where humanity survives.
- The Doctor and Tegan drink mead with Susha and Cuther.
- The Doctor knows a version of the story of Noah's Ark in which Noah had to leave behind unicorns, centaurs, basilisks and many other such animals.
- This story equates the end of the world seen in The Ark with that mentioned in Frontios.
- Mark Gatiss is miscredited here as "Marc Gatiss".
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