I don't agree with most responses here. Yes the transaction is yours, but it's really about the 'intent' and 'spirit' of the transaction. Did the seller 'intend' on giving you an animal that was gravid? Would the seller have behaved diffrently had they known this information beforehand, yada, yada, yada...
If you go to the bank and cash a check, and the teller gives you too much money, that in and of itself, doesn't allow you to keep it. It would not be the bank's actual intent, and to knowingly take the money and keep it doesn't alleviate you from the fact that you have retained money improperly. - Albiet most would, and banks have tried to collect in these situations, and often win in court. I know this is probably a bad example because of the regulations imposed on banks, violation of public trust and so on, the point is:
I realize that neither of you knew, and you have every right to keep the clutch and move on...I just wanted to share a differing view point. Congrats though
just my 2 cents