That's a great piece of animation. I don't know if the content-less opening and ending are there to be true to an original film reel or something along those lines, but for those who haven't visited the link it's about seven minutes of animation.
Set the playback speed to 2X, and it's only 3.5 minutes. Viewers must've been more patient in the 1960s.
That would ruin the timing and deprive the viewer of the subtlety in the animation. The single-frame transformations into animals and the connecting frames while the camera's perspective pans would be almost impossible to distinguish. This is art, not a lecture. Digesting the series of events in the most efficient way possible is not the point. No one cares how the story ends, it's nice but trivial compared to the animation itself.
Beautiful animation, but was there supposed to be any significance to the plot? Wikipedia suggests it's some sort of biblical allusion but I don't see how it relates.
The ending (during the credits) seems to allude to Noah's Ark, but I'm grasping at straws trying to make the rest of it work toward the Story of The Great Flood.
Maybe Noah, in his search for two of each creature, sets this up to find a mate for his Box Creature, as well as for himself?
The Ark is a socially acceptable way of animating the fact that they are sexual partners and gives a clever explanation to the fact that the clothing throughout the animation suggests that it is raining. The story starts by making it look like a parlor trick for free drinks then develops into what looks like a sadistic prank but it ends up finding an endearing resolution that puts everything right. Let the animation speak for itself, pigeon-holing is a fool's errand.