Valmiki Ramayana Sundara Kanda Sarga 56 Shloka 15

घोरैः with dreadful ones, आशीविषोत्तमैः with poisonous snakes, निःश्वसन्तमिव as if hissing, नीहारकृतगम्भीरैः with majestically covered heavy mist, गह्वरैः with caves, ध्यायन्तमिव as though meditating, controlling all senses.

The mountain was as though hissing like a dreadful, poisonous snake. With the caves standing majestically covered with mist, the mountain appeared as if it was meditating.