Cobras, a type of snake, can traverse water, as well as hide beneath corpses and other objects the player might come across in the dungeon. While not the most dangerous serpent one might find, the blinding attack combined with poisonous bites can pose a serious problem if other creatures are around.

Encyclopedia entry[]

Darzee and his wife only cowered down in the nest without
answering, for from the thick grass at the foot of the bush
there came a low hiss -- a horrid cold sound that made
Rikki-tikki jump back two clear feet. Then inch by inch out of
the grass rose up the head and spread hood of Nag, the big
black cobra, and he was five feet long from tongue to tail.
When he had lifted one-third of himself clear of the ground,
he stayed balancing to and fro exactly as a dandelion-tuft
balances in the wind, and he looked at Rikki-tikki with the
wicked snake's eyes that never change their expression,
whatever the snake may be thinking of.
'Who is Nag?' said he. '_I_ am Nag. The great God Brahm put
his mark upon all our people, when the first cobra spread his
hood to keep the sun off Brahm as he slept. Look, and be

[ Rikki-tikki-tavi, by Rudyard Kipling ]