Animals

Though sleuth-like readers will soon figure out that the mystery creature referred to here is actually a train, Dickinson uses an extended metaphor to depict the train as a kind of super-powerful, foreign animal. This reminds readers that the train moves through the natural world, but doesn't belong to it. The train is personified with various creaturely traits; as we read it, we might compare it to a whole menagerie of different animals. However, all of these familiar characteristics eventually only make this manmade beast seem all the more strange and extraordinary.

• Lines 1-4: The train-animal (tranimal?) is obviously a ravenous one; it doesn't simply travel along, but rather gobbles up miles and valleys, before feeding itself (that is, refueling).
• Lines 11-12: The train is a vocal creature, and the description of its complaints in "horrid—hooting stanza" (12) emphasize its wildness and incomprehensibility. The alliteration here ("horrid," "hooting") highlights the uncivilized quality of its speech; think of an owl hooting creepily in a dark forest, or hyenas laughing wildly.
• Line 13: There's a kind of fun, puppy-like quality to this line; the train "chase[s] itself downhill" the way a playful pup might chase its tail.
• Lines 14-17: Here, the train is a horse. It neighs loudly and returns peacefully to its stable. The simile Dickinson employs in line 14 is also a bonus Biblical allusion ("Boanerges" is an Aramaic nickname that Jesus once gave two of his vociferous disciples. It means "sons of thunder").

Furthermore, Dickinson's crisp alliteration ("star," "stop," "stable") brings a kind of clipped precision to this stanza, kind of like a horse trotting briskly home.