Nothing is off-limits to Dave when he is in investigation-mode. He will literally go anywhere and put his nose in anything in order to solve a mystery. He really is just as dedicated to his investigations as he is to napping, as hard as that is to believe. He even knows how to open full-sized doors, which is not a universal cat skill. Here you can see that Dave has infiltrated the area underneath the kitchen sink and is sniffing around for clues. Some horrible grating noise was emanating from there, so Dave went to investigate.