How do voice actors do this?

[Petzbreeder]

I just watched a Behind the Scenes Spongebob Squarepants video and I have to say, voice actors really surprise me sometimes.

Skip to about 50 seconds into this video and try not to die laughing!

Seriously, how does he do that? How does ANYBODY do that?

[sylar]

i make that noise pretty easily when i see straight people irl

[Mockery for One]

Oh...

Oh my God...

The video, maybe?