What is a metaphor in "The Open Window"?

"It is quite warm for the time of the year," said Framton; "but has that window got anything to do with the tragedy?" (Saki)

The open window becomes a symbol or representation of the tragedy.  The open window is compared to a memorial to the supposed dead hunting party.  Even though Saki does not make this explicit comparison, Vera makes it clear that the window remains open because of the tragedy. 

The simple open window is transformed into a ghoulish door between life and death. Vera's look of horror creates the metaphor, without any words necessary.

"The child was staring out through the open window with a dazed horror in her eyes. In a chill shock of nameless fear Framton swung round in his seat and looked in the same direction." (Saki)