Work on your content.
VOICE-ACTORS
I think you should employ some. These are two human-like characters, and I think they can benefit from some personable voice-acting.
PLOT
There wasn't really any-- save for the brief dialouge before the gag.
HUMOR
It was a gag--- a rather poor one. If it's quick gags you're after, I would recommend reading up on some of the ones Disney did in the early 1900's. Perhaps read a book on humor, or buy a book of your favorite comic strip.