The Lord of the Rings: The Fellowship of the Ring
When Gandalf visits Bilbo, Gandalf was to bump into a candlestick to show how small Bilbo is in comparison. What wasn’t planned was Gandalf hitting his head on the roof beam, which became a great punchline to the moment.
I live near very near to LA; I know people who work in the film industry. Around here, a lot of people would have firsthand knowledge of that sort of thing, so it wouldn't be unusual to hear from someone who knows something such as that.