Snakes are elongate, legless, carnivorous reptiles. Dr. Jennifer Keller once had a live snake implanted in a cadaver she was working on at med school by a fellow student. (SGA: "Doppelganger")
While under the affect of an Alien tick Airman Dunning believed there was a snake under the skin of his arm, which he tried to claw at and ripped the skin from his arm. (SGU: "Pain")
Colonel Jack O'Neill often refers to Goa'uld as 'snakes' or 'snakehead'.