More specifically, people are raving about part of one verse where Slim Shady begins rapping at what he refers to as "supersonic speed."
The lyrics are really tough to make out.
Here they are below.
Via Rap Genius:
"Uh, sama lamaa duma lamaa you assuming I'm a human
What I gotta do to get it through to you I'm superhuman
Innovative and I'm made of rubber
So that anything you say is ricocheting off of me and it'll glue to you
I'm never stating, more than ever demonstrating
How to give a motherf---in' audience a feeling like it's levitating
Never fading, and I know the haters are forever waiting
For the day that they can say I fell off, they'd be celebrating
Cause I know the way to get 'em motivated
I make elevating
What's so impressive is that Eminem spits these ten lines of lyrics - 97 words - in 15 seconds.
That means he's averaging six and a half words per second.
Insane.