"A distinctly macabre streak appears in the art of the inhabitants of Tlatilco, possessed by a psychological bent that delighted in monstrosities. To illustrate this point, one might mentions such representations as two-headed persons, or heads with three eyes, twos noses and two mouths; hunchbacks; idiots; horribly ugly and sometimes masked individuals who may be shamans; and many other outrageous deformities. Several actual clays masks have been found, of the most sinister appearance; a few of these are oddly split vertically into two distinct faces, one of which might be a skull, for instance, and the other half an idiot with a protruding tongue. Let it be noted here that dualism, the unity of basically opposed principles such as life and death, constitutes the very basis of the later religions of Mexico, no matter how great their complexity. Here we see the origin of the concept."

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