here's a story for you. a friend of mine had a pregnant cat and after the given time gave birth to one rather large kitten. just a normal black and white moggy but as there was only one it was very big. the following day she gave birth to 2 tiny kittens that looked like they were some kind of oriental cross. big pointy faces and huge ears. they looked like little aliens, had hardly any fur and you could see all the markings on their skin. as they were so tiny she took the 3 kittens and mum to the vet and the surmised that they were 2 different litters. that the mum had ovulated again probably about 2 weeks after getting pregnant, had mated again and the birth of the first kitten had dislodged the second 2. he was very surprised because although he'd read about it he'd never actually seen it. when i saw the kittens i was gobsmacked. the difference between them was unbelievable, it was obvious that they werent the same litter. all three kittens survived btw.