Based on the details provided, the two correct answers that would likely be included in the middle of the plot diagram for the story "Dusk" by Saki are:
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After the young man leaves, Gortsby finds a cake of soap lying on the bench and believes that the young man left it there.
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After listening to his story, Gortsby accuses the young man of lying because he cannot produce the cake of soap that forms part of his story.
These details are essential to the development and climax of the plot, showcasing key events that lead to the resolution.