Survivor Contestants 'Drop Like Flies' – and Jeff Probst Tells PEOPLE All About It

Okay, watch the above exclusive Survivor preview showing the Survivor: Kaoh Rong episode 4 immunity challenge in which contestants have to run through obstacles and dig through sand for bags. We've seen it dozens of times before.

No big deal, right?

Wrong.

CBS has released a second video, seen below. This is 45 minutes later. All hell has broken loose.

Survivor's medical team has to tend to several castaways who have collapsed in the triple-digit heat. It looks like chaos.

But here's the thing. We knew this was coming. As the season began, host Jeff Probst talked to PEOPLE about the brutality of the entire season – and of this challenge in particular.

What are the conditions like out there?
We've never had a season that punished the players like this season. The heat is oppressive.

Did that come as a surprise?
There's always a good way for me to gauge how difficult the season is going to be, and that's how the crew members do before taping. And we lost more crew members this season than any other season. And when I say lost, I mean crew members who had to be sent back to the States to get treatment.

Treatment for what?
Most of those came from infections that got really bad. I always want to explain. When I say infection, in your head, you think, 'An infection? I've gotten infections. They aren't that bad.' But when you're in the jungle, an infection can become life-threatening very fast. We had crew members who had infections cut out because they had spread so fast and they needed to control it.

Wow.
I know. Wow.

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So did that make you nervous?
It did. It was not an easy 39 days. It was so difficult that I spent all of my day and all of my night monitoring the radio, just to keep tabs on what was happening on the beach, which is not normal. Normally I'm not checking in at all because things are going fine. The conditions were so tough that everyone was on high alert for the entire time.

But isn't there a worry that this will ruin the show? If everyone is using their energy to survive, there won't be strategy or a social game.
No, that's not really the way I would put it. When you have harsh conditions, especially heat that drains you, it impacts the gameplay. It doesn't remove it; it changes it. It's another obstacle they have to overcome. It makes the game more unpredictable. People have shorter fuses. They're less able to move six moves ahead; they have to think just two or three moves ahead.

Does the heat affect everyone?
There's always someone in the corner, sitting in the shade, saying, 'I'm doing just fine. Heat doesn't get to me. I'm going to dominate.' There are definitely very big moves and gameplay. There are some real betrayals coming up.

How does the heat affect challenges?
A lot of what we do is pretty simple – go through the obstacles, dig up the puzzle pieces, do the puzzle. If you're comfortable and well-rested, that should be a piece of cake. But it's not 75 degrees out, and you're not rested and fed. So suddenly, you're struggling in 100-degree heat to do something that you could do a hundred times at home. That's what we see. It's not that the challenge is brutal; it's that the challenge combined with the heat is brutal. And they drop like flies.

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So let's pretend that you, Jeff Probst, are playing this game in the heat. Would these conditions make you play more conservatively?
No. I know it's hot. I know it's miserable and you're uncomfortable. But you've got play this game hard. If your motive is to play conservatively, you can probably do that and get to the final five. You can go home and brag to your friends that you made if far, but you're not going to win.

I'm not interested in sacrificing 39 days of my life and getting my ass destroyed so I can tell people that I did pretty well. I want to win, or I want to go down swinging. Those are the people I look for on the show.

I wouldn't want to put something on my mantel and tell my kids, 'Yeah, did did pretty well and made the final seven.' Screw that! Your dad swung for the fence and struck out – or he swung for the fence and won.

So you'd play all out, even if it's 110 degrees?
Absolutely. Why else would I play?

Survivor airs Wednesdays (8 p.m. ET) on CBS.