Her head was sometimes seen as a hydra when depicted with four heads, known as the Tetrakephalos “the four headed Hecate.”
“From whence they (viz. the Chaldean tradition) hand down the mystical doctrine concerning the four elements and four-headed Hekate. For the fire-breathing head of a horse is clearly raised towards the sphere of fire, and the head of a bull, which snorts like some bellowing spirit (daimonion), is raised towards the sphere of air, and the head of a hydra as being of sharp and unstable nature is raised towards the sphere of water, and that of a dog as having a punishing and avenging nature is raised towards the sphere of earth.” Wunsch, R. trans. 1898. John Lydus’ Liber De Mensibus. Leipzig, pg 4 in reference 61.
61 Ronan, S. 1992. The Goddess Hekate. London: Chthonios Press, pgs 79 – 150
The Symbols of the Goddess Hekate