We’ve seen the promos that show Russell Swan collapsing on tonight’s episode of Survivor: Samoa in the middle of a challenge. And we’ve heard Jeff Probst in those promos describe it as “the scariest moment I’ve ever had on the show.” Well, after getting an advance look at the episode, I can tell you this: Probst is right — it is scary. Like, hand-over-the-mouth scary. I can also share some inside scoop that challenge producer John Kirhoffer provided a few weeks back on what went down. The incident takes place during a reward challenge called “Roll With it.” The challenge is adapted from a similar challenge from the Cook Islands season called “Monkeys in a Barrel.” In this one, blindfolded tribe members are directed through a course by someone who is being rolled inside a giant “Helio-sphere.” The blindfolded members then need to roll a small ball through a table maze. From the promos, you can clearly see that Russell is one of the blindfolded contestants. So what causes Russell to collapse? According to Kirhoffer, massive dehydration is to blame. (You’ll have to tune in tonight to see if medical ends up pulling him from the game or not.) As for the other big question of what happens to the rest of the challenge, Kirhoffer revealed two things: The challenge was not reset and finished, and while it was not played through to completion, “you can be sure that we will be playing it again someday, somewhere in the future.” (Hmmm…seeing as how season 20 was also shot in Samoa, I’d wager that will be sooner rather than later.) In the meantime, want to see the challenge for yourself? Then check out this exclusive video of Jeff Probst running a rehearsal of “Roll With It,” and — super Survivor geek alert! — see which former Survivor fave has a niece now working for the show testing out challenges. The answer awaits in the video below! Oh, and don’t forget that I’m now on Twitter just waiting to be followed @EWDaltonRoss.