Dawson Casting: Millie Perkins, who portrays 13-15 year old Anne, was nineteen years old when she got the part.
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.