OOC.
There is a question, in cases like this, of whether player knowledge can substitute character knowledge. I, too, think I know the answer OOC (and yeah, now you mention it Sasyra, I think it is in The Hobbit!), but there's an argument to be made for the character being an avatar of the player and as such any player knowledge or ideas are fair game for the character. Of course, where this strays into metagaming things like monster knowledge (e.g. trolls and fire) is an area to be mindful of.
Just some thoughts on the subject.