Almost all of the children's books by Ted Geisel ("Dr Seuss") were written in rhymed couplets. One of the very few exceptions was 'The 500 Hats of Bartholomew Cubbins', which Dr Seuss wrote in straight prose. Freed from the constraints of rhyme and metre, Geisel was able to write a deeper and more complex story here: one of his very best books. (Even better is the sequel, 'Bartholomew and the Oobleck', which is also written in prose.)
The 1943 movie version is an animated short, produced by George Pal in his virtuoso stop-motion animation technique which he called 'Puppetoons' ... in which a flexible armature body is moved one frame at a time, whilst a series of individual heads (with slightly different facial expressions) are placed on the body's neck. This technique was remarkable and distinctive at the time, but has since become overfamiliar from its use in other venues, such as in the Pillsbury Doughboy adverts.
Most of Pal's Puppetoons are quite funny (occasionally marred by some racial stereotyping) and can be enjoyed by children and adults even today. 'The 500 Hats of Bartholomew Cubbins' manages to be clever rather than funny. When this movie was made in 1943, audiences were likely impressed more than amused ... and nowadays they're not likely even to be impressed, as animation techniques have improved so much.
There are some distinct changes from Seuss's story. In Seuss's original book, Bartholomew Cubbins is a boy who wears a small red hat. When the King rides by in a carriage, Bartholomew loyally removes his hat ... but an absolutely identical little red hat instantly appears in its place on his head. When he removes this second hat, an identical third hat replaces it... and so on, well into the 400's of hats. From this point, the hats gradually become more complicated: one hat sprouts a feather, the next has two feathers, until the 500th and last hat becomes very elaborate indeed.
In Pal's animated version, EVERY hat after the first one is extremely elaborate, and each hat is different ... so that we get no sense of them becoming increasingly complicated. Since the Puppetoon mannequins and their props are three-dimensional physical objects (not animated drawings), it's amusing for us to see these huge bespangled chapeaux popping out of nowhere underneath Bartholomew's tiny original hat, but Seuss's original dramatic progression is lost. When the King's servants stuff Bartholomew into the carriage and drive away with him, he leaves a long trail of hats behind, each hat looking utterly different. This is about as funny as the movie gets.
I'm a fan of George Pal and a fan of Dr Seuss, but they both did much better work elsewhere. I'll rate this animated short 4 points out of 10. Most modern kids are too jaded to like this sort of thing.