Answer and Explanation:
In his poem "O Captain! My Captain!", Whitman provides clues about the unnatural death of the captain when he mentions the blood dropping on the deck of the ship. People who die naturally - of natural causes - do not usually bleed. Bleeding is the result of being hurt, injured, be it in an accident or due to violence.
<em>O the bleeding drops of red,
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<em> Where on the deck my Captain lies,
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<em> Fallen cold and dead.</em>
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As we know, the fallen captain is none other than Abraham Lincoln, who had been shot and killed. The whole poem is a metaphor for his death as well as the victory of the Union in the Civil War. Whitman is lamenting Lincoln being gone, having been murdered before he could see and celebrate victory with the country.
