Have the butcher slice the beef, veal and pork into wafer-thin, bite-size slices. Or slice the meat at home; this is easier if the meat is slightly frozen.
Slice the kidneys into halves and remove the hard cores. Cut the halves into thin slices.
Divide the meats, onion and sauces equally among six plates. Provide each guest with a long, wooden-handled, two-pronged fork.
Pour the stock into a chafing dish, electric saucepan or deep heatproof serving dish. Bring the stock to a boil in the kitchen, then place it over an alcohol or other burner in the center of the dining table. The stock must continue to boil while the meal is eaten.
The object of this exercise in dining is for each guest to spear a piece of meat and lower it into the boiling liquid until cooked to the desired degree of doneness. (Pork must be well cooked.) The cooked meat then is dipped into the chopped onion and sauces.
If desired, serve rice as a side dish. After the meat is eaten, the cooking broth is served as a soup course.