Naturally, the mummified fetus is not viable, but it happens so that the rest of the litter can be born normally without any ill effects to the mother from carrying around a dead fetus. It happens
in most animals, and can even happen
in animals that only have two or three babies, like goats and sheep. Mummified foals have even been born along with a live twin.
The red blood thing has me a bit worried, though.