But, more seriously, why should someone realize what's happening if they have no prior knowledge of the aeserpent? It doesn't make too much sense, unless the venom just makes them thirsty for blood, in which case you should need something more like a save to resist drinking blood rather than a check.
Besides, you can use Heal untrained.
Even magic should make some sense.We don't have to make the same mistakes as the original designers (or worse yet, some editor who messed with the original design).
You could maybe convince me to go for an untrained Knowledge check, but I still prefer Heal and Knowledge as usual. Besides, I think we have you outnumbered.
EDIT: What I'm trying to say is that the original designer probably picked the Int check out of a lack of better options. The use of skills in 3.X to notice things gives us more versatility and better options even without going to exception-based design.
I vote version #1.
Updating Working Draft.
We've still got "Like all creatures of the Beastlands, darkstrikes are not subject to spells which affect animals, even snake charm."
Should we do something with that?
As magical beasts, they should be immune to most spells that affect normal serpents.
Yeah, I was leaning toward that solution, but did wonder whether we should widen it to some kind of limited resistance to Enchantment spells.