Fists are so much easier to draw with only four fingers, if you ask me.
I went through some of Jeffbert's screen caps of the '60's series (which are lovely) for more reference material. I came across this:
I'm sad nobody seems to have translated it. Whatever it says, Ochanomizu seems to find it annoying.
And he just pushes it off screen! I love it. Cartoons are just something else, aren't they?
Now, if you'll notice, he has four fingers here, but in the very same scene a few seconds earlier:
Five fingers! Maybe he lost one when he sneezed.
Awp! Never mind. It's back.