Gygax discusses just this in his DMG (p 81):What bothers me about the exhaustion/luck/skill HP thing is that spider/viper bites etc. still inject poison - which implies at least some physical contact. So I think any wound which deals damage has to make some kind of actual contact or injury (however minor), but higher HP characters mitigate it (not avoid it - that's AC).
The so called damage is the expenditure of favor from deities, luck, skill, and perhaps a scratch, and thus the saving throw. If that mere scratch managed to be venomous, then DEATH. If no such wound was delivered, then NO DAMAGE FROM THE POISON.
In other words, you don't have to narrate a given degree of hp loss the same every time. If other mechanical consequences only make sense if physical injury occurred (say, poisoning) then that is part of your narration. If not, then physical contact need not be part of the narration. The narration is flexible, provided only that it conforms to the constraints imposed by whatever the mechanical outcome happens to be.
This is [MENTION=37579]Jester Canuck[/MENTION]'s Rorschach test in action; this is what I mean when I say that hp, at least as put forward by Gygax (and then refined in 4e) are not a simulationist mechanic. (One semi-technical label for this sort of mechanic is "fortune in the middle" - you roll the dice first, and then establish afterwards, via narration within the parameters set by the dice - eg the saving throw that failed or not - what happened in the fiction.)