NPCs, PCs, and ESP

[Muz]

(Acronym alert!)

So here's a question for all the DMs out there: What do you do in a situation where you've got an NPC (or just a creature of some sort) with the ability to read surface thoughts of the PCs? More specifically, has anyone come up with a good method of doing this in a way that DOESN'T tip off the players to the fact that their minds are being read? Some players are good at not metagaming in that situation, but I figure it's always better to avoid giving a metagaming temptation if at all possible.

So, thoughts? Ideas? Clever anecdotes?

[Comet]

Ooh! Me! Pick me!

So.
The PCs were chasing this mysterious bad guy that they knew to be some NPC they knew in disguise. They finally catch up with him and force him to reveal his face.

The trick was that his guy had the power to appear as the person that the observer was expecting to see instead of his true self.
As the players were ready to see the villains face, I called a short break for drinks and snacks.
During this break, I asked, in a completely metagame fashion: "So, [player x]who do you expect this villain to be?"
The players go: "Yeah, he'll definetly be that important guy who's been trying to mess up the status quo in the city's court. [Jackass aristocrat Y], wasn't his name?"

We resume gaming and lo and behold. The villain turned out to be [Jackass aristocrat Y] and then promptly fled, leaving the players with the feeling of "we'll catch him next time."
Of course, when they confronted [Jackass aristocrat Y] later on, he knew nothing of this mysterious villain. This marked the beginning of a sweet game of cat-and-mouse-and-mindscrewing.