The evildoers do not expect an answer to their question because they think no one will see them. AT: "No one will see what we are doing" (See: [[rc://en/ta/man/translate/figs-rquestion]])
The writer speaks of man's "inner thoughts" and "hearts of man" as if they were a deep body of water that no one can explore all the way to the bottom. (See: [[rc://en/ta/man/translate/figs-metaphor]])