Answer:
They indicate an otherworldly atmosphere around the narrator.
Step-by-step explanation:
Mark Twain's "A Ghost Story" is a ghost story about how the narrator experienced during his stay at a hotel. The story seems to be based on the Cardiff Giant, a monster carved out of stone and buried in the ground, only to emerge oftentimes to 'scare' people.
The narrator reveals how he heard "muttered sentences; half-uttered screams that seemed smothered violently;" during his first night at the "old building". This tone, with the discovery of the "[footprint] so vast that in comparison [his] was but an infant's" presents an otherworldly atmosphere, a sense of horror and suspense. By using these words to describe the sounds he heard along the hallway while listening intently, the narrator presents us with a scene that is scary and even intriguing.