In this kind of situation, the PC's either would know the catch or the won't.
Honestly, I don't think there are many cases where this will come up. I mean, if you are facing them off against a "fluted milfonky" (lol--yes, completely made up) then they will have no idea. However, if you have any kind of creature that can, for instance, suck blood, drain life essence, etc. you will have a character that goes "that sounds similar to x,y,z" and starts trying things.
These days there is a great deal of talk and media representation for the supernatural. Joe Shmoe may hear "chupacabra" and think "I saw that on X-Files". The media tends to mix up <ahem> "truth" and fiction, but that is the point. I really think that lore should give a sliding scale of information. You may not get the catch, but you might have an idea...
Now regarding actually running it, I don't think it should be a complete exchange, unless the creature is using powers to guide the character's mind away from the truth. I think you make anyone, wizard included (wizards don't know EVERYTHING, but they know more than others which is what the Lore skill represents), make a lore check automatically on being given a reason to believe that the creature is not human, but yes, adjusted based on what the creature is doing. For DnDers, this would be like a disbelief check on illusion. Later in the scene, for instance, if you get more data, then I would let them do a similar 'quick check' as a supplemental action again modified for how much they have seen (remember they will probably be running under incorrect info more often than not, unless a creature really shows its full abilities). It doesn't take any time, really. If a character has a hunch, they can take a full exchange to really examine and search their memory. Otherwise, it is 'hey, the way he went up that wall didn't look natural.' But that still isn't a lot to go on for a lore check. Transform into a dragon and you've got more to work with.