Though the concept of this movie is obviously very far fetched and invovles technology that does not exist, it seems to me there was a crucial error in the fact that Castor Troy (Nicolas Cage) and Sean Archer (John Travolta) have different blood types. Even with super-advanced lasers and other methods of doing the face transplant, the fact that one blood type is O- and the other is AB would completely negate the abilities of that technology. I may be mistaken, but wouldn't Sean Archer's body absolutely, undoubtedly reject Castor Troy's face from the blood type difference alone? Or are we just supposed to overlook that and assume that the technology overrides biology in this situation?