Bawylie
A very OK person
There's one very obvious problem with asking the player to describe how they're doing something. Sometimes the player knows more than the GM about a subject in the Real World. If their RW knowledge isn't applicable, then how can they answer the question without your input?
Let's take the poisonous mushrooms question from the OP. If I tell you I'm looking for a valvo, do you know where and what that is? What colour are the gills? Is there red on the cap or stem? There are other things I'd look for examining a mushroom, but that's two simple ones. You can certainly stop the game to look up what those things mean, or maybe you know the answer, but then there's an awful lot of subjects where it's not easy to find information on some things and you won't know the answer. How do you then determine whether the player is suggesting something reasonable and adjudicate accordingly?
That's why you ask for action and intent. "What are you trying to do, and how do you go about it?"
Also, we don't pretend conversations suddenly stop after the player declares something. If I'm not clear what you want or what you're doing, I'm going to ask follow up questions, not just shrug and say "Well, since I don't understand what they want or what they're doing, I guess I can't DM anymore."
-Brad