Shabbat 110 - Water left uncovered
In Babylon, where snakes were abundant, there was a danger that water left uncovered might have been drunk by a snake, who could leave there its poison. For this reason, the Sages prohibited drinking any water that was left uncovered for enough time that the snake hiding behind the vessel might have appeared and drunk from. In other times and at other places this law should not apply, but it has mystical connotations, and is discussed often in the Talmud.
What is a cure for a one who drank water left uncovered? - It is made of a tree used for shepherd's staff. If one does not have it, he should take five roses and five cups of beer, and boil them together. A certain man drank uncovered water. The mother of Rav Achadvoi cooked roses in beer and made him drink it in a hot oven, and poison came out of him like a green leaf of a palm branch.
Alternatively, they should bring a sweet etrog , carve out a hole in it, fill it with honey, then cook it in burning coals, and he should eat it. The Talmud then discusses what to do when one swallows a snake, or when a snake enters a woman.
Art: William Oliver - A snake in the grass