Later in his life, Sagan's books showed his skeptical, naturalistic view of the world. In his book "The Demon-Haunted World", Sagan gave a list of mistakes he had made as an example of how science is self-correcting. The compilation "Billions and Billions: Thoughts on Life and Death at the End of the Millennium", published after Sagan's death, contains essays written by Sagan, such as his views on abortion, and Ann Druyan's account of his death as a non-believer.