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 sign was an eagle perched on a serpent.
Actually, the sign was an eagle perched on a cactus, eating a serpent; the partially correct statement fooled the model.
( z1 eagle :ARG1-of ( z2 perch :ARG2 ( z3 serpent ) ) :domain ( z4 sign ) )