The Gemara goes into much detail about how one should not leave liquids uncovered lest a snake deposit its venom. From what little I know about snakes, I do not think they leave venom in this way. The gemara already prohibits various beverages etc. for fear of non-Jews using them for libations etc. so I doubt that the snakes are a metaphor for something else. So why does the gemara go into such detail about snakes, and is their concern realistic based on current scientific knowledge?
Richard Dine, Silver Spring, Maryland, USA
There are two issues here. One is whether snake venom is harmful if ingested. This is generally considered not to be the case (unless there was a small internal cut or tear that would allow poison to enter the bloodstream). I do seem to recall reading that cobra venom is harmful by ingestion, but on the other hand, mongooses eat the venom glands of cobras that they eat, without suffering any ill effects (and this is not due to any immunity - if the cobra bites the mongoose, it will die).
The next issue is whether snake venom could conceivably be left on a glass after the snake drinks from it. I cannot claim any expert knowledge in this area, but it seems vaguely possible, if the snake had recently eaten and still had drops of venom that it had already secreted from its glands and were in its mouth.
Kol Tuv,
Natan Slifkin
If venom can enter the blood through cuts in the lips or tongue, there is cause for concern to make a Gezeirah.
Aside from that, it is possible that Chazal had other health concerns in mind aside from just snakes. In the more primitive sanitary conditions of the past, contamination of water sources was always a major concern.
Mordecai Kornfeld