According to tradition, they founded Tenochtitlan ( "Place of the High Priest Tenoch" ) after much wandering when they saw on an island in Lake Texcoco the sign that their god Huitzilopochtli had indicated -- an eagle perched on a cactus, eating a serpent .
The serpent was a rattlesnake.
( z1 snake :mod ( z2 rattlesnake ) :domain ( z3 serpent ) )