Scientists have carried out a successful head transplant on rats ahead of plans to attempt a similar operation on a human later this year. 

During the procedure, the head of a smaller rat was attached to the body of a larger rodent. Rather than simply replacing the head, the team attached the donor head to the body of the larger rat, creating an animal with two heads.

The operation involved three rats in total: the donor, the recipient and a third used to maintain the blood supply to the transplanted head.