Always check your props before going on stage. You know, so you don’t accidentally use a real knife and damned near kill yourself.
Did anybody watch the HBO series “Oz”? There’s a similar Shakespeare moment when the prisoners are performing Macbeth, and one prisoner takes out the other by switching a real blade for the fake.
By the way, the story linked above is not a Shakespeare play…but it is about Mary Queen of Scots, so I guess there’s a bit of a stretch connection :).
Bonus points for astute readers who remember this story about Brutus stabbing himself when a similar mixup occurred.