His Gait — was soundless, like the Bird —

His Gait — was soundless, like the Bird —
But rapid — like the Roe —
His fashions, quaint, Mosaic —
Or haply, Mistletoe —

His conversation — seldom —
His laughter, like the Breeze —
That dies away in Dimples
Among the pensive Trees —

Our interview — was transient —
Of me, himself was shy —
And God forbid I look behind —
Since that appalling Day!

Emily Dickinson

The answer is a cast-off skin of snake. Emily composes much poetry of weird things, disgusted by successful poets of romantic school.

The only ghost I ever saw
Was dressed in Mechlin lace,
So he wore no sandal on his foot
And stepped like snowflakes.

His moving was silent like the bird
But rapid like the roe deer.
His costume is quaint, mosaic
Or by chance, mistletoe —

His conversation was seldom.
His laughter was like the Breeze
That was absorbed in hollows
Among the thoughtful trees.

Our interview was brief.
He was shy of me,
And God forbid I review it,
Since that appalling Day!

Appalling day is referred to “Paradise Lost”. The snake tempted Adam and Eve to eat the forbidden fruit so that they were expelled from Paradise.