
Suddenly his breathing was fast as a hummingbird’s heartbeat suddenly his fingers were clenched tight as old roots around a rock. In the next instant it metastasized into a bone-chilling terror that froze him solid. He had a few seconds’ warning: a sudden formless disquiet spreading through the gut, an anxiety that his civilized neocortex tried to write off as simple acrophobia.

Little readouts, logarithmically spaced along the bulkhead, pegged the gravity-0.3, 0.25, 0.2-as he rose. The belt drew him up through a series of telescoping segments hazard striping highlighted the spots where each handed off to the next, where the bore of the tunnel increased by some fractional increment.

It's described earlier in the book in more detail:Įven under power the ascent seemed light-years long, an infinite regression of rungs and rings and bulkheads that almost seemed to breathe when he wasn’t looking.

The 'Zone of Terror' refers to is a strange, unreasonable panic that the character feels when he's ascending on the conveyor belt.
