I know with National Geographic's website you can go through their listings and have them email you when a show you want to see if coming on. Maybe Discovery does the same or has online listing you can view. I just usually flick through and end up doing the "Mike come quick it's something on about snakes!!!!" thing LOL

I did a bit of research and apparently it's not that unheard of to become somewhat immune to venom. Here's a quote from a website on the Quail Ridge Reserve talking about this very thing.

"California ground squirrels have evolved immunity to the venom of western rattlesnakes. In populations sympatric with rattlesnakes, adults are relatively immune, while juveniles and populations outside the range of rattlesnakes are susceptible to venom."

I know it wasn't ground squirrels on that show so it seems another rodent has figured out how to get around the predators in their lives at least to some degree.