What is "rhythm", as it applies to drawing, exactly? There may be a definition written down somewhere, but I don't know where. Preston Blair touched on it in his second book on animation, but it's a little confusing (to me, anyway). Maybe rhythm is in the eye of the beholder. Maybe it means something different to everyone, but I think the drawing of the rabbit on the upper left does seem to have rhythm, while the peanut-shaped fox and lion on the middle right don't seem all that rhythmic to me.
The closest thing to a good examination of the concept of "rhythm" is this chapter on "Curves from the book "Bodyworks". Marbury Hill Brown wrote this book about life drawing, and it's an interesting book because it's a book about drawing that's mostly full of drawings, not text. What a revolutionary concept (these pages are full-page spreads but I didn't put them back together because it would have taken forever). Click to see bigger and read them.
This book really seems to make the point that a drawing with an "S" curve is a sure-fire way to create rhythm in your drawing. Think about it: straight lines don't really have rhythm, and a curved line has some rhythm, but as "S" curve always has more rhythm that the other two kinds. Luckily for us, most living forms seeem to be constructed along the lines of "S" curves. In humans, it's to keep all the forms stacked on top of each other and yet have them all stay balanced. Of course, as you animate or storyboard, it would be impossible to always draw your characters in "S" curves, just as human beings don't always form an "S" curve. When we bend over to pick up a quarter we become more of a simple curve, etc.
Rhtyhm seems to be about creating a "rhythmic" line of action and putting all the parts along that line.
Richard Scarry's drawings don't necessarily have a lot of rhythm to them. They are rarely based on "S" curves and they almost never have a very dynamic "line of action". But they are still appealing drawings.
Part of their charm, actually, seems to be that they don't ever get too extreme or distorted, even when his characters are involved in violent action.
Well, anyway, that's as close as I can come to telling you what I know about "rhythm". To make things even more confusing there is another definition of "rhythm" used in art that I will define some other time!