Author may want to implement a labelling method for users for a days to maybe train the discriminator a little bit better. Would be a cool human-in-the-loop exercise.
Even in this[1] difficult comparison you can see the non-human repeating skin patterns on the right and the awkward teeth contour. Also hair-on-skin often looks wet and with unnatural bends.
When comparing wrinkly people then it gets a little harder.
Look at the clothes and necklace. The clothes are different on left and right sides of her face - the moment you see it you can't unsee it and it's obviously wrong.