Metamorphosis is one of the oldest animation techniques. When character animation evolved, however, metamorphosis fell out of fashion and was basically limited to shape-shifting characters and two-dimensional objects. Yet some filmmakers still liked to use it now and then for gags. It is no surprise that such gags were popular with Bob Clampett considering his highly fluid character designs.
In THE SOUR PUSS (1940) both Porky and his cat morph briefly into a fish and a chicken respectively just to get across which animal they are "talking" about.
Just focus on Porky for a moment: He is clearly a cartoon character like Goofy. He might have the head and tail of a pig, but dresses and behaves like a simplified human of baby proportions.
The cat however is closer in style to Pluto, the pet dog, than to Goofy, the human character with a stylized dogface. So when Porky becomes a fish it looks a lot stranger than when the cat behaves like a chicken, with only minor changes in appearance.
While Porky looks like a human baby with a few pig features attached, Daffy Duck simply looks like a skinny boy/man stuck within a duck suit. We don't think for one second of his arms and hands as wings. And even when Mr.&Mrs. Daffy Duck (as they are called in THE WISE QUACKS, 1939) live in a barn among other farm animals, Daffy is not for one minute behaving like a duck.
It's interesting that in Clampett's films ducks - in contrast to chicken in the same films - in general look like humans in duck suits as can be seen in WHAT PRICE PORKY (1938):
Realism vs. Cartoon
In early Looney Tunes, four-legged animals often walked and moved as if they had human anatomy. In fact, most of the time it looked as if two set of human legs moved in cadence. It is one thing to depict a camel as an ambler - they are actually able to amble on purpose - but when it comes to dogs, it looks like the animators simply weren't experienced enough to convincingly draw four-legged animal locomotion and made the best of it.
However, even with these limitations Clampett emphasized the difference between "realistic" animal behavior and "cartoony" human behavior. Within split seconds these animals can change their anatomy and appearance towards humans with freaky heads. Remarkably, it is only then that we accept them as true characters and not just animal sidekicks. It seems that they can only express their personality in quasi-human form with a voice and distinctly human hands instead of paws or hooves.
In most of these films, such a change is the reaction to a narrative event. In PORKY IN EGYPT (1938) the camel is infected with desert madness by a malevolently violent sun.
|An ambling camel starts to move like a long-necked man with strong hands.|
|Apart from the head and the hunches, the camel morphs into a madman.|
|The whole episode ends in the reversal of the two characters' relationship: now the camel is leading (actively carrying) Pork and not the other way round.|
|In THE FILM FAN (1939) the snobbish dog ambles past a lifelike poster of a forest...|
|...and suddenly turns into a human in a dogsuit walking on two legs with hands instead of paws.|
|From evil monster with scary teeth to typical Clampett smile with just one "silly-character" tooth.|
|From ill-disposed scavengers to barbershop quartet (decades before THE JUNGLE BOOK vultures).|
|Wartime work horses in MEET JOHN DOUGHBOY (1941).|
No matter whether they walk or dance on two or four legs: The protagonist and his love interest in THE HEP CAT (1942) adopt human behavior from head to toe - especially toe:
|The creepiest element: a female cat with incorporated high heels.|
In PORKY'S POOCH (1941) an Irish dog is again walking on four and standing on two legs but also has to tighten his belt:
When some of the animal disguises are destroyed by a story event, the human bodies underneat may look unexpectedly skinny as in PREHISTORIC PORKY...
The crazy face: In one of those zeitgeisty running gags any character could adopt the looks of comedian Lew Lehr uttering ".... is the cwaziest people" in his trademark accent.
|PORKY IN EGYPT (1938), THE SOUR PUSS (1940), RUSSIAN RHAPSODY (1944).|
The human version: Even realistically caricatured Hollywood stars like Lauren Bacall (BACALL TO ARMS, 1946, [UPDATE: actually picked up by Art Davis after Clampett left the studio]) can unexpectedly morph into cartoon versions of themselves when perform broader actions.
The reversal: There is a rather funny gag in CRAZY CRUISE (1942), a cartoon Clampett took over from Avery. The camera pans along a queue of realistically drawn jungle animals to reveal their very human behavior of drinking from a marble water post.