Old 30/40s cartoon about a murder mystery

Couple of very memorable visual gags in it:

The detective pulling a fake hair of the edge of the screen as if it was trapped int he projector.
Same detective reaching out of the screen to hit a silhouette of an cinema audience member shuffling to get to their seat.
Same detective (again) taking one super long stretchy step into the background of the image

...and I think a repeated animation of bodies (skeletons?) falling out of a cupboard over and over again until one of the stops and says something about their being "rather a lot of them."

It's the hair and silhouette gag that I remember it for, but I imagine the rest of the cartoon must be very good to feature two great fourth wall jokes.

Any help, greatly appreciated!