Some things in life just shouldn't be mixed -- smoked salmon and, say, cotton candy, for example. Plaid shirts with paisley shorts. Arnold Schwarzenegger and the Queen's English. The music of death-metal mavens Carcass and the hip-hop flava of Missy Elliott. All are combinations that make little sense.

But when you're Chad Boltz, mixing and matching some of today's biggest pop stars with some of the earliest architects of grindcore and industrial metal makes perfect sense -- you've just got to have the ear for it.

Boltz, a mash-ups aficionado who lives in Denver, said it dawned on him one afternoon while he was working at one of the Mile High City's independent record stores. He was listening to a Boom Selection compilation CD of mashes and figured if artists like Jay-Z and Linkin Park could be fused together, perhaps some of storied metal label Earache Records' catalog could be intertwined with pop acts like Destiny's Child and Sean Paul.

"I thought it would be kind of cool to remake some of the old-school Earache stuff that I listen to, like the old grindcore stuff, with pop, because they're just so different," explained Boltz, a guitarist who once played in defunct grind band Monistat 7, which released the album Now Available Without a Prescription in 1994. "I listen to a wide range of music, so I don't mind pop so much. I figured putting the vocals to metal songs might sound interesting."

His experimentation led to seven monstrosities that he posted online. Links to his Web site, xxx.reek.tv/x.htm, popped up on heavy-metal message boards, and in no time the elite were calling for his head. His site was ill-equipped to handle the increase in traffic, and Boltz's domain was crippled for more than month.

While he said there's no reliable method to measure just how many people downloaded the free tracks, Boltz said the songs continue to make the Internet rounds. While he's proud of all of the mash-ups -- including Outkast's "Bombs Over Baghdad" crossed with Entombed's "Sinners Bleed," Shakira's "Whenever, Wherever" spliced with Napalm Death's "Suffer the Children," and 50 Cent's "In Da Club" paired with Terrorizer's "After World Obliteration" -- his favorite is Destiny's Child's "Survivor" merged with Godflesh's "Dead Head."

"The industrial tracks are easier to swallow than the grindcore ones, because the tempo changes aren't as frequent," he surmised. "It turned out really well, but it's much harder than people think. I tried forever to do stuff with Bolt Thrower, but the tempos change too much. It's the same with most metal songs, actually."

Of course, not all of Boltz's experimentation yielded listenable results. One mash-up he thought for sure would come out superb was Beyoncé's "Naughty Girl" meets Korn's "Shoots and Ladders."

"It ended up sounding like two songs being played at the same time," said Boltz, who's putting the finishing touches on his latest musical Frankenstein's monster: Kelis' "Milkshake" bonded with Ministry's "Thieves."

Surprisingly, none of the labels for the pop star victims of Boltz's creations have contacted him about the mash-ups. But he did get an e-mail from Earache founder Digby Pearson. "He just said he doesn't understand why I did it," he said. "He told me it was a good idea that didn't work out, and that metal never needed to be fused with this music. But if any of the big labels [for some of the pop acts] have a problem with it, that's fine. I'm not making any money off of this. I just want people to download them -- that's the spirit of mash-ups, really. But if they want them down, oh well."