Trivia: Ronald Lacey, who played Toht in Raiders of the Lost Ark, cameos as Hitler's top adviser, Heinrich Himmler, during the book-burning sequence.
Trivia: 2,000 rats were bred specifically for this film, particularly for the scene in the Venetian catacombs. The producers wanted disease-free rodents and ordered them from the same company that previously supplied snakes and critters on set. When the rats were being burned, mechanical rats were used instead.
Trivia: Before getting the role of Walter Donovan, Julian Glover had auditioned to play Colonel Vogel.
Trivia: Kevork Malikyan (Kazim) had previously auditioned for the role of Sallah in "Raiders of the Lost Ark" (1981).
Trivia: Vogel's name is never spoken in the film. It is only mentioned in the closing credits.
Trivia: Despite his prominent billing, John Rhys-Davies does not appear until 53 minutes into the film.
Answer: Henry says, in response to Indy asking if he remembered the details of the trials: "I wrote them down in my diary so that I wouldn't have to remember." So, obviously he did NOT know them by heart. Also, as the other answer says, they didn't want the diary to either be in the Nazis' possession or be burned.