The term 'MULTIHEADED SERPENT SLAIN BY HERCULES' is referring to the mythical creature known as the HYDRA. The HYDRA was a nine-headed serpent that was slain by the Greek hero Hercules as one of his twelve labors. The HYDRA was said to be immortal, and each time one of its heads was cut off, two more would grow in its place. Hercules eventually overcame the HYDRA by burning the stumps of the heads after cutting them off.