These are almost too painful to browse through:
Drinking and hangover can cause temporary double vision, especially for those who drank more than they should these holidays. But double vision can be also achieved with the effects of Photoshop.
To show the effects of double vision, take any celebrities or politicians and double their eyes and mouth at the same time. Do not double a nose as it will ruin the effect which comes from our brains refusing to accept that part of the face (eyes & mouth) is doubled, but part (the rest of the face including nose) is not. Of course you will need to extend a chin and upper part of the face a bit to fit the extra mouth and eyes.