Why does Valli refuse to look out of the window on her way back?

Valli was every enthusiastic and excited throughout her journey. But on her way back home she refused to look out of the window because she saw a young cow lying dead by the roadside. It had been struck by some fast-moving vehicle. It was the same cow that was running in front of their bus, during their trip to the town. She was overcome with sadness. The memory of the dead cow haunted her and therefore, she refused to look out of the window.

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