Continuity mistake: At the end of the show, Tony is making an ice cream sundae for himself and A.J. He gets a Path-mark store brand aerosol can of whipped cream. When the camera cuts to closer look at Tony the can changes to a Redi-whip brand of whipped cream. (00:49:00 - 00:50:00)
Continuity mistake: While Tony is talking to Melfi about A.J, Melfi's lipstick color darkens halfway during the conversation. (00:12:37)
Answer: That's not Jimmy, just a look-a-like. Jimmy's short and stout, the guy in "Christopher" episode is tall and medium built. The hair is also different.