Final answer:
Suspense is built through Zaroff's calm explanation of hunting humans, which contrasts with Rainsford's growing horror, using vivid description and imagery.
Step-by-step explanation:
One literary device that builds up suspense when Zaroff is explaining the most dangerous game to Rainsford is the use of vivid description and imagery. Through Zaroff's calculated and mysteriously calm demeanor in detailing his hunting of humans, the reader senses Rainsford's growing horror and disbelief, which heightens the tension. This technique is similar to the suspense created in other narratives when characters face realizations that turn peaceful or familiar settings into scenes of dread or impending danger.