There's a lot of debate online about whether or not EMINEM was LIP-SYNCHING when he performed on "Saturday Night Live"this weekend. And, I guess, whether or not it matters if he was.
Eminem hasn't commented . . . and there wasn't really any one moment that "proved" that he was faking it, but he did seem offbeat at times with his rapping.
It's a complicated issue, partially because . . . according to multiple sources . . . there's typically a separate mix for broadcast that's different than what the audience THERE would hear, and those mixes aren't always on point.
There could also be some glitches in the sound and picture, even if it's a "live" broadcast. On top of that, Eminem's first performance, "Berserk", includes multiple layers of vocals, so it's hard to decipher what's him . . . what's being sampled . . . and what's part of a backing track.
Regardless, Eminem's career was BORN out of his dominance in live rap battles, with all kinds of improvisation and intricate, complicated freestyles . . . so he would seem like one of the least-likely rappers to accept lip-synching. Or NEED to do it.