"The X Factor" boot camp: What you don't see

They don't call this week's "X Factor" competitions "boot camp" just for fun. According to season one finalist Chris Rene, it's called that for a reason. Even Simon Cowell described Wednesday and Thursday's rounds as "a nightmare."

And behind-the-scenes, the contestants are put through the ringer a bit, too.

"They don't show that part," Rene told CBSNews.com. "I was there. I know what it's like."

On Thursday's part-two of boot camp, contestants teamed up with partners to perform a duet; one member of each pair will be eliminated. In these kinds of high-pressure situations, there's forgetting of lyrics and shedding of tears.

"The point of this challenge is very simple, which is: be better than your opponent," Cowell told the hopefuls Thursday.

"I remember boot camp -- you stay up really late," Rene said. "You barely sleep. You barely eat, and you have to perform. They want to see who can handle it and who can't. They give you Pepsi, which you're not supposed to drink when you're singing. And Doritos, and you're not supposed to eat corn. They give you the stuff that kills your vocal cords. It's boot camp."

Next week, "The X Factor" returns with results of the second boot camp task. That means the field will be narrowed from 60 to 24 contestants, who will be invited to the judges' homes for the next competition round.

Because this is pre-taped, the contenders already know their fates and whether they've been invited back to the homes of judges Britney Spears, Demi Lovato, Simon Cowell or L.A. Reid.

"They already went through it. They already know who's going to the judges' houses," said Rene, who just released his debut album, "I'm Right Here." "All the people that made it know, and all the people that didn't know...I remember it was so crazy."

The competition heats up in November when the live rounds begin.