The character played by Chip Zien is listed as Jeff Robbins in the end credits but is named Jeff Warren in the episode; he even spells his name for Norm.
After Norm picks up his first beer, the head is shown to fill almost half the glass, yet when it cuts back a second later, he has a beer with a normal sized head.
As Frasier is sitting at the bar, you can hear the door being opened behind him even though it does not move.