Michael Silverbane
Adventurer
Disagree. Player motive for uncle Rusty injection is completely different to the one I stated.
Player motive is completely irrelevant to the adjudication of the action declaration. If we're ruling out degenerate play (i.e. someone cheating or being a jerk), then the resolution is the same, regardless of motive. There is (to me) no functional difference.
We are discussing actor and author stances and whether the player temporarily moves from one stance to another in this specific situation (character knowledge).
I don't find that distinction either necessary or useful. More important (again, to me) is the question of whether the game covers the actions and its resolution.
In some versions of D&D, there are rules covering if and how much useful knowledge of a creature a character might posses, so it is appropriate to consult those rules when such an action declaration is made.
In some other games, there are no such rules, so some sort of ruling about such questions should be reached.
Maybe it is determined that such knowledge is in no way important or useful (i.e. Trolls and other monsters are not specifically vulnerable to any particular attack, nor are they particularly invulnerable to any form of attack). Maybe it is determined that any such knowledge is widely known and automatically recalled. Maybe it is determined that characters know what the players know. Any which way, the table will have to figure it out for themselves.