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Tear Jerker: Withnail and I
Monty's farewell letter to "his boys" is incredibly sad.
The sight of a despairing Withnail trudging away in the rain is haunting.
While not in the film itself, the published script has one in its foreword. In it Bruce Robinson recounts tales of himself and Vivian (the man Withnail is based on) back in the 60s. It's all fun and games until the final paragraph, where it drops the line "And I can't believe Vivian is dead. He got cancer of the throat and they tore his voice out." The rest is absolutely heartbreaking.
Marwood's fare-well: "I shall miss you, Withnail."
The fact that only a pack of wolves know just how good an actor Withnail can be. Especially that in the original ending Withnail kills himself with a shotgun.