Richard Gordon:
The author of the original books (and of the screenplay here) is on screen hidden behind the anesthetist's mask in the "patient wakes up" scene. Gordon did the job in real life before turning to writing.
When Sparrow takes the letter from Sir Lancelot out of its envelope, the letter is folded into four, yet when he takes it out of his coat pocket when in the pub, it is folded in three.