I bought this postcard years ago, in the pre-internet days. I found it in a box today, while looking for something else. We saw this (enormous) painting in Rouen, and nobody in the museum could tell us what on earth was going on in this strange scene. We were intrigued, even asked the waiters and the chef in the restaurant that night. Nobody knew. "Les énervés de Jumièges", there is a lunatic asylum in Jumièges, maybe the painting had to do with that.
But now, in the internet days, a Google search reveales everything. It is a very famous painting, about a very well known legend. Inspired artists from Simone de Beauvoir to Salvador Dali, there's even a movie about it. Apparently we met an incredible number of ignorant people that day in Rouen.
Here you can read about the legend in English.