Grass vipers were a type of animal, a variety of snake found on the planet Bajor.
History and specifics[]
In the year 2318, Jas Holza compared the Cardassians to grass vipers as they were always watchful and careful, but yet always hungry. He also thought that the Cardassian's grey skin made the comparison even more accurate. (TLE - Terok Nor novel: Day of the Vipers)