What you do is you take lines from different poems (or different parts of the same poem) and rearrange them to make a different one, like so;

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The grieved are many, I am told; (Dickinson)

So sad, so fresh, the days that are no more. (Tennyson)

Deep as first love, and wild with all regret; (Tennyson)

While the Weary Blues echoed through his head. (Hughes)

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The second day of mourning is always grey, (Gaston)

For all that is done and said. (Yeats)

He then becomes a man of woe; (Blake)

And slept like a rock or a man that's dead. (Hughes)

No man is an island. (Donne)