Luke: How did my father die?
Obi-Wan: A young Jedi named Darth Vader, who was a pupil of mine until he turned to evil, helped the Empire hunt down and destroy the Jedi knights. He betrayed and murdered your father.
When the stormtroopers break into the control room, the stormtrooper on the right of the screen hits his head on the door frame. On the DVD release they've added a thump when he hits it.
On its initial release, the film was booked in just 37 theaters. It ended up breaking 36 house records.