The One With Barry & Mindy's Wedding - S2-E24
Corrected entry: In this episode, when Ross and Rachel are at the wedding, there's a couple, "Mr. and Mrs. Weinberg" that approaches and tells Rachel that he's happy to see her and he hardly expected to see so much (because in that episode Rachel walks down the aisle with her butt showing). The lady is actually another extra from another episode, the one where Chandler quits. It's the same lady who goes and tells Chandler about their boss wanting to talk to him.
Correction: Extras are often used in multiple episodes.
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