Jail Bait Wait: A meta example. David Kross, who played the younger Michael, was seventeen during filming. They waited until after he had turned eighteen to film the sex scenes.
What Could Have Been: Kate Winslet was the first choice for Hanna, but had to turn it down due to scheduling conflicts with Revolutionary Road. Nicole Kidman was then cast, and they put the project on hiatus to allow her to star in Australia. After she had finished that, Nicole dropped out because she was now pregnant. In this time, Kate Winslet had become available again.