It's amazing how many vintage cartoons contain zombie audience scenes like this one (above) from Clampett's "Henpecked Duck."
Look at the audience behind Daffy. The characters in the background painting are hazy and ghost-like, with blank faces as if they were just bussed in from Hell.
Here the audience has acquired some definition but they're still engulfed by an eerie mist and are lit from only one direction. Why did so many old-time directors favor this kind of weird treatment? The obvious answer is that drawing each individual head in the crowd would have been time-consuming and take too much attention away from the main characters. Look at these sharply-drawn Jack Davis heads (above). I don't know about you but I spend a lot more time looking at the faces in the crowd than the people in the car. So that might be the answer.....but it's not the only possible answer. Maybe zombie audiences were just plain funny.