Serpent

Serpent is a word of Latin origin (from serpens, serpentis "something that creeps, snake") that is commonly used in a specifically mythic or religious context, signifying a snake that is to be regarded not as a mundane natural phenomenon nor as an object of scientific zoology, but as the bearer of some potent symbolic value. Snakes have been associated with some of the oldest rituals known to humankind.

[http://en.wikipedia.org/wiki/Serpent_%28symbolism%29]

The caduceus (play /kəˈdjuːsiːəs/ or /kəˈdjuːʃəs/; from Greek κηρύκειον kērukeion "herald's staff" ) is the staff carried by Hermes in Greek mythology. The same staff was also borne by heralds in general, for example by Iris, the messenger of Hera. It is a short staff entwined by two serpents, sometimes surmounted by wings. In Roman iconography it was often depicted being carried in the left hand of Mercury, the messenger of the gods, guide of the dead and protector of merchants, shepherds, gamblers, liars and thieves.