Final answer:
The question does not correspond to the provided text excerpts as there is no mention of characters named Kevin and Joules, or any incident occurring outside a spa bathroom.
Step-by-step explanation:
The question you've asked doesn't refer to actual content from a specified book or story, as the references concerning Kevin, Joules, the spa bathroom, and the chomping, rustling sound are not present in the provided text excerpts.
In the given material, several instances of characters hearing strange or unsettling sounds are mentioned, but there is no specific incident involving Kevin and Joules witnessing something outside of a spa bathroom.
In each excerpt provided, different characters experience different events: John hears a sharp noise and sees a figure, Venters hears a low roar, McTeague hears night noises and sees his birthday gift, Deborah hears no noise at all.
Nippers suffers from indigestion, a wallet is found with the smell of a lion on it, there is concern about Peter and Wendy's whereabouts, George Hadley picks up something near where lions had been, Venters wakes up to the music of mockingbirds, and someone listens through a crack in a cell wall.
These experiences are distinct and do not align with the scenario you've described involving Kevin and Joules.