Poem:

I like to see it lap the miles,
And lick the valleys up,
And stop to feed itself at tanks;
And then, prodigious, step
Around a pile of mountains,
And, supercilious, peer
In shanties by the sides of roads;
And then a quarry pare
To fit its sides, and crawl between,
Complaining all the while
In horrid, hooting stanza;
Then chase itself down hill
And neigh like Boanerges;
Then, punctual as a star,
Stop — docile and omnipotent —
At its own stable door.

Question:
The poet could have just described the train itself, but she chose to describe it as though it were an animal. Why might the poet have described the train as an animal? Use details from the poem to support your answer.