re: A riddle to get your brain going this morning... (Now NSFW)

A sane human (truth) and a sane vampire (liar) would both say they are human. George says he is human, so he is sane.

An insane human (liar) and an insane vampire (truth) would both say they are a vampire. Adam says he's a vampire, so he is insane.

So we know for a fact that they are not both sane or insane, which makes Adam a liar. Insane humans lie, so Adam is human.

No more information is presented to clarify if George is a sane human or sane vampire. We are told that half the population is human and the other half vampire, but that doesn't mean a sample of any two people will result in having one vampire and one human. There is not enough information to determine if George is human or vampire.