How do the words muttered sentences, half-uttered screams that seemed smothered best enhance the tone of this passage

They indicate an otherworldly atmosphere around the narrator.

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.

i love to sleep it's the best

as for symbolic actions, the narrator's tearing down the wallpaper in an attempt to find the "woman" in the wallpaper represents her struggle to retain or regain her sanity.   the wallpaper has been part of her confinement and by her tearing it down, she is freeing herself from that confinement.