Harsher in Hindsight: A number of Anne's innocuous musings on the end of the war and what she wants to be when she grows up are considerably harsher in view of the real life Everybody Dies ending to the story.
Paranoia Fuel: Being cramped and crowded in a small space while you are constantly fearing for your life. The inhabitants must remain completely quiet ten hours every day, not moving a muscle. Even the most minor mistake (such as flushing the toilet at the wrong time) can mean the end. If that wasn't terrifying enough, every scene where they are nearly discovered is this.