When Rachel says, "Mister Waltham, I need to speak to you," he says, "In a moment, I'm in the middle of a task," and is holding two suit jackets in one hand. When the camera cuts to another angle, he has them in both hands.
After Monica lures everyone to their new apartment with cookies Phoebe pours milk several times into the same two glasses.
Rachel complains to Monica that she just helped an elderly woman try on a thong and she didn't purchase it. Customers have never been allowed to try on undergarments such as thongs and knickers for sanitary reasons.
Prior to watching Cathy's play, a quick clip is shown of the Circle in the Square Theatre. This theater is known for being one of the only Broadway theaters designed "in the round," meaning the audience surrounds the stage on all sides instead of just one side like a standard theater. However, immediately after is a shot of Chandler and Ross taking their seats in a theater that's clearly not in the round.
Stage lighting is seen in the reflection on the tv in Rachel and Monica's apartment.