For curious monolingual folks like myself, the labels on those bags (haricots de Soissons) indicate that they're full of beans. You can see a similarly NSFW example of a postcard referencing General Oku Yasukata here along with the following explanation:
...In French, "au cul" means "at/on the ass." Thus, as Linhart explains, "Oku" and "ass" are homophones in French, restricting the pun to a play on the French figure of "General Ass."
That's part of what keeps me coming back here. Sometimes it's just a simple joke and a crude Photoshop, other times you get a nice trip down some rabbit holes.
I'd like to think the academics are just happy to see people taking an interest in the material. No reason history has to be stuffy and boring.