We started with raw chicken breast over the weekend, and now we're up to the feet, and later today I'll go get some pre-killed mice for them to gnaw on. Ewww. Still, they're carnivores, in fact:
Ferrets are primary, obligate carnivores with a gastrointestinal tract so adapted to flesh digestion that they can hardly tolerate the ingestion of vegetable foods. A primary carnivore is one which eats mostly flesh, and an obligate carnivore is one which must eat flesh to obtain essential nutrients.
They have absolutely no need for the grains and carbohydrates in kibble, they can't digest grain, and they should normally get their energy from fat and meat protein. Too many carbohydrates is what's giving American ferrets a scourge of insulinoma, a disease that is rare in European ferrets -- which are usually fed meat.
They also need all the parts of a critter. The intestines, brain, heart, liver, bones, even the hair.
UPDATE: We gave them the mice. Callidia tore the head off hers first, crunched it up loudly, and ate the whole thing, bones and all. 
Been a fan since '80 and finally got to see them live.
They opened with "Johnny hit and run Pauline"
First encore opened with "Blue Spark"
Second encore opened with "The New World".
Great great 'effin show. Just thought you'd like to know.
Rock on.