When the Doctor, Susan, David and Tyler are looking over the cliff, the Doctor leans against a rock, the wobbling of which reveals it to be made of polystyrene. See more
One day, I shall come back. Yes, I shall come back. Until then, there must be no regrets, no tears, no anxieties. Just go forward in your beliefs, and prove to me I am not mistaken in mine. Goodbye, Susan - goodbye my dear.