The central image is the original, un-butterflied, face. The image to your left shows the persons right side butterflied and the one to your right shows the left side butterflied.
Apart from the obvious width difference (which may be caused in some faces by the slight turn of the head on the neck) did you notice the subtle differences? Maybe the slight upturn to one side of a mouth that on first glance looks symmetrical? Or the difference in the lines on the face or the angle of the eyes? Take another look.
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