An artist (Georges Méliès himself) is going to paint a portrait of a dummy. No, he wasn't going to paint an idiot, it was a mannequin. Anyway, there's a young woman who wants to fool the guy and substitutes herself with the dummy. Unfortunately, the artist is such a dummy himself he can't see it coming...until it's too late.
Considering it's a pretty basic gag, the execution is very good for a single joke and makes it work as well as it could. The main reason this short isn't funny today is because...well, nobody laughs at artists attacking mannequins anymore. Méliès knew audiences of the time would enjoy it, but now it comes off as unfunny despite good execution. I'll still give it credit as good comedy for 1900, because it works well for the time, but the piece is too dated now to be funny so it's mainly of interest for people like me who enjoy these early movies.