Karl and Lisa as you've never heard them before

We all know the high-pitched effect helium has on a person's voice, but a YouTube science star has given the TODAY Show hosts a taste of the exact opposite.

Nick Uhas, an LA-based TV host who has earned a global following through his online science explainer videos, appeared on the show today to conduct several experiments with the pair.

After showing hosts Karl Stefanovic and Lisa Wilkinson how Doritos can be used to fuel a barbecue, he then gave them a balloon full of sulfur hexafluoride, a gas that is five times denser than air.

The effect was instantaneous, with Wilkinson letting out "hi" in a deep baritone.

"That's just so sexy! That's the best thing ever," Stefanovic said, before taking over the balloon.

"You're watching TODAY right across Australia, this is unreal," Stefanovic bellowed in the hilarious voice.

"Ha ha ha yeah smokin'."

Uhas finished off the segment by letting Wilkinson perform the world's first shattering of a dry ice frozen watermelon "jack-o-lantern".

It was a perfect hit.

"See that's how you do it Michael Clarke," she said.