I'm not an Asian native either, but the liquid isn't going to hurt me. As skoogenheimer noted, the first issue would be the animal would need to get its head into the pitcher, and a boa of any kind is going to find that hard with all but the largest traps (and I have never heard of any snake referred to as a "garden boa." "garden snake" perhaps, but both are incorrect terms not applicable to any species). Second issue would be the snake would be more likely to look for food than find water there, as again they can smell the difference quite readily. Thirdly, if it were (as terrible a thought it may be) the only source of water, there is nothing in the liquid of a Nepenthes that is going to have a detrimental effect on a snake; they don't secrete toxins into the fluid (or nowhere near the amount that it would take to hurt a snake the size of a Corallus species), and the enzymes won't hurt an animal with already powerful gastric fluids anyway. Anything in there wouldn't be much different beyond that from a puddle in bromeliad, which this species would find in situ.....