From a Jeff Probst pre-season interview for Fiji re - how the HI was changed after Cook Islands:
The Slug: Tell us about the Hidden Immunity Idols. There's two this season, but how are they used?
Jeff Probst: I think we figured out how to do it this season. The very first time we introduced it, you had to play it before anybody voted. Then the second time we introduced it, you could play it after the votes had been made and read. So it was an absolute get-out-of-jail-free card.
This season, I think we found the happy medium. You must play the Idol after the votes have been cast but before I read them. Before the votes, I say, "How confident are you? Do you want to take a chance? Or should you play your Idol?" That made a dramatic difference. The Idols get played. Nobody is sitting on their Idol until the end and taking it home as a souvenir.
