What is superfetation?
Superfetation involves the simultaneous occurrence of more than one stage of developing offspring in the same animal. In other words two pregnancies at the same time, but where the babies are different ages.
Some animals such as rabbits and hares have two wombs or bipartite wombs, allowing them to expect two different litters at the same time. Superfetation is also known from rodents, horses, sheep, cats, and some marsupials. The existence of superfetation differs from breed to breed and from species to species, but it is not the normal state of any mammal.
A rabbit womb might include two different litters at the same time.