The expression was that of agony—the agony of intense bodily pain; but a menace scowled upon the brow, and a few sprinklings of blood added to its ghastliness. Yet it was not all these characteristics—it was some horror of the mind, some inscrutable antipathy awakened by this picture, which harrowed up my feelings. What technique does Irving use to build suspense in the excerpt?

The pace of the story quickens.
The word choice darkens the tone.
Odd characters are introduced.
The setting details are intentionally omitted.