Serpents had a great symbolic value to Aztecs, and were considered sacred animals, probably on accoun of them being to renew themselves by changing their skin, a fact which was seen as a passage to a higher level of essence. In Nahuatl language the serpent is Coatl, a word that appears in fact in the names of the major Aztec deities.
A pectoral plate with this double-headed serpent was probably used by Aztec priests during magical rhytes.
Requested by Vincenzo.