Cage's odd reaction inside that killer's house?
As he creeps about, with that eerie, screechy 'music' going on, trying to find 'Machine', he starts to go downstairs again, but as the music stops and restarts, instead of pausing and checking visually, he immediately turns and marches confidently back up?
Wouldn't even an armed PI be more careful and wary, being in the dark, creepy home of a huge sadistic killer?