Drybrush was a tool old time animators sometimes used for speed effects. Here Clampett took it as far as possible and made a joke of it.
You had to be a really good inker to pull this off.
The effects style of many old cartoons were designed to match the medium, to look cartoony and appropriate to the graphic style.
Today we have major studios competing to see who can have the most realistic backgrounds and the most realistic film effects. (It's actually an imitation of the blurs that film creates when an object is moving too fast to photograph clearly. It's not realistic at all.)Why you would want "realistic" effects in a cartoon is one of the mysteries of the ages anyway.
Here's a carefully animated subtle scene of Bugs Bunny talking to a man's buttocks.
Note the hard-to-draw tilt of his head below. Here's where your toy construction! studies will come in handy.
http://www.cartoonthrills.org/blog/Clampett/WackyWabbit/drybrush02small.movThe animation is really great too. You can actually feel Elmer's weight bouncing around, even though it's all a blur. Go through the clip in slow motion and be amazed at the skill.
Bugs sure likes to access Elmer's goods.Look how alive Bugs is in the older pre-tude cartoons. He really was a wascawwy wabbit back then. Compare to just 4 years later