Who Killed Who? is one of the early Tex Avery MGM Cartoons, created in 1943. The short is a pastiche of whodunit cases.Beginning with an announcer proclaiming the cartoon as an educational example of how crime doesn't pay, it is set in an old, spooky house on the "Gruesome Gables". The elderly owner is murdered and, seconds later, a crafty detective arrives to investigate—but he finds out that the house is a haunted and wacky place, where finding and unmasking the murderer might prove very problematic.
The cartoon short provides examples of:
Black Cloak: Worn by the killer, along with a black mask.
Born in the Theatre: Done with a black silhouette of a "theater patron" who moves around despite the detective's order of "Nobody move!", followed by him knocking out the guy with a "That goes for you too, bub!"
By the Lights of Their Eyes: Parodied when the eyes visible beyond a door peephole are left shut out when the peephole closes abruptly, forcing them to knock on the door to be let back in.
Creepy Changing Painting: Of a comedic variety, of course—a painted woman in a bathsuit who has hastily covered herself by the time the detective peeks at the painting again.
Dem Bones: A regular skeleton, and a red one (a Shout-Out to comedian "Red" Skelton). Earlier on, a skeletal cuckoo in a clock calls out the time.
Obviously Evil: As a gag, when the detective pushes a button marked 'RING BELL FOR SUSPECTS', the butler, maid, and chauffeur come in- and they all look rather sinister. It then turns out that they're actually pretty cheerful.
Detective: Which one of you bumped off the ol' man?! Whodunnit?!
Suspects: Awwww, wouldn't YOU like to know!
Peek-A-Boo Corpse: A closet that holds hundreds of corpses that fall out one by one, for (presumably) a very long time. Lampshaded:
Random corpse: Ah yes! Quite a lot of us, aren't there?
Also when the detective is taking a picture of the body covered by a sheet. The victim sits up and poses, then falls back under the sheet. The detective lifts up the sheet:
Victim: Let's not get nosy, bub.
Roger Rabbit Effect: Sort of - the live-action and the animated characters aren't seen together, but some clever cutting in the ending makes it look like this.
Show Some Leg: The detective resorts to this to catch the killer.
Spinning Clock Hands: When the victim receives a message that he is going to die at midnight, he looks terrified at the cuckoo clock; there's still a few hours left, but then the hands suddenly spin all the way to midnight.
Steal the Surroundings: After the Extended Disarming sequence, the detective says they'll try it again. He turns out the lights, and when they come back on everything in the room (including the bookcases and pictures on the wall) is gone.
Surprise Santa Encounter: Unbuilt Western version: the detective sees a door marked "Do Not Open Until Xmas". Scoffing, he opens it, and runs smack into a very irritated Santa.
Wrap Around: The detective drops a vase into a pit in the floor; after a while, it falls on his head from above. Later on, he himself falls into a pit on the ground floor and, after a lot of noise, comes crashing down the stairs that lead to the upper floors.