the US Army Medical Corps errs in using as its symbol a caduceus with two snakes. The caduceus of Aesclapius the god of healing had only one snake

In ancient times [my parasitology professor informed the class lo these many years ago] removing a long parasitic roundworm from under the skin was not simple. If you gave it a yank it would snap and re-grow; the only way to get the whole thing out was to apply a steady gradual pull. (As with Silly Putty.) So the practitioner had to attach one end to a stick, apply gentle tension, and gradually wind the worm around the stick as it slowly emerged. When the last length came out, you had a stick with one coil wrapped around it. Voila! the Caduceus, symbol of the healer.