I remember learning somewhere that the upper class in France prior to the French Revolution would often eat bizarre foods, just for the shock value, similar to how celebrities and wealthy people in modern times do weird stunts to get attention.
One food in particular I remember hearing about was, "bird stomachs," however, when I tried searching, "Did the french aristocracy eat bird stomachs?" or even, "cooked bird stomachs," on Google, the only results are relating to bird anatomy -- not exactly what I'm looking for.
So, did they really eat bird stomachs? What are some other bizarre foods that they ate?
I can't answer right now about "bizarre foods" eaten by French aristocrats, but bird stomachs were not one of them because they were not bizarre. Animal offals are less consumed nowadays in industrialized countries where there is an easy access to "noble" parts, but, when abundance was not a thing, people were very into recycling and circular economy and avoided throwing out things that could be reused. Food offals would be turned into stews, broth or pies if edible by humans, or into animal feed if not, or put in a manure/compost heap if not edible by animals.
Birds do not have a stomach like ours, but their digestive system includes several organs, notably the gizzard, which acts as a mechanical stomach that "chews" food thanks to its tough muscular walls (and bits of gravel in some cases). Poultry offals, known collectively as giblets in English or abats/abatis/abattis (and sometimes menu) in French, include the digestive tract as well as other parts: liver, kidneys, heart, feet, neck, wings, combs etc. English and French cookbooks from the 18th century offer a variety of recipes to prepare giblets and turn them in proper dishes. Here is one:
The Art of Cookery Made Plain and Easy: Which Far Exceeds Any Thing of the Kind Yet Published, by Mrs Hannah Glasse, 1747.
To stew Giblets. LET them be nicely scalded and picked, cut the pinions in two; cut the head, and the neck, and legs in two, and the gizzards in four ; wash them very clean, put them into a stew-pan or soup-pot, with three pounds of scrag of veal, just cover them with water; let them boil up, take all the scum clean off; then put three onions, two turnips, one carrot, a little thyme and parsley, stew them till they are tender, strain them through a sieve, wash the giblets clean with some warm water out of the herbs, &c.; then take a piece of butter as big as a large walnut, put it in a stew-pan, melt it, and put in a large spoonful of flour, keep it stirring till it is smooth; then put in your broth and giblets, stew them for a quarter of an hour; season with salt: or you may add a gill of Lisbon [wine], and just before you serve them up, chop a handful of green parsley and put in; give them a boil up, and serve them in a tureen or soup-dish. N. B. Three pair will make a handsome tureen full.
The Cook's and Confectioner's Dictionary, by John Nott, cook to His Grace the Duke of Bolton, 1723
To make a Ragoo of Giblets. SCALD the Giblets, and if you have any Cocks combs, scald them by themselves, and skin them ; then put them into a Pan with strong Broth, seasoning them high with Salt, Spice, and sweet Herbs, and simmer them ; then fricassy them in melted Bacon, with some Cives and shred Parsley ; then put them again into their own Broth, and simmer them, thicken with the Yolks of Eggs, and serve them up in Plates.
Similar texts can be found in French manuals and cookbooks (Encyclopedia of rustic economy, 1770), which also turn the giblets into stews, pies, broths, soups and other dishes where they are thoroughly mixed with other ingredients. Alexandre Dumas, in his own posthumous Grand dictionnaire de cuisine (1873), considered turkey giblets to be one of the best dishes of bourgeois cooking. He did not like gizzards, though, because he found them too tough and tasteless, but the fact that he includes them in his dictionary shows that they were indeed consumed. Gizzards are still eaten today in France though they are usually sold separately. Duck gizzards in confit are a popular (and delicious) dish that one can find in supermarkets.
Now, the term "bird stomach", in 17-18th century French, also meant "the flesh of the bird left when thighs and wings are removed" (Furetière dictionary, 1701; the dictionary of the Académie Française still included that definition a century later): at that time, estomac was a general word for the thorax and the abdomen (today that would be only the abdomen): "bird stomach" in that context would just mean "poultry breast", and it is used in that sense in the dictionary of domestic economy of Louis Liger, which mentions "partridge stomachs" and "capon stomachs" (1723). But then there is nothing bizarre here either.