Monica tears open the second gift revealing a brown box. The gift switches from being wrapped to being unwrapped between several shots.
When Monica is opening presents, she's wearing a necklace, then when she turns it's gone, and then when she turns again she's wearing the necklace.
When Phoebe is telling Rachel that telling the father is like ripping off a band-aid she rips one off her arm. In a scene later on back in Monica and Chandler's apartment the band-aid is back on her arm.
When Monica is unwrapping presents, and Rachel and Phoebe are there, talking, every time the camera changes focus to them, the box in Monica's hands is unwrapped, but when the camera is back on her, the box is still in the paper.
Ross asks Chandler if the flowers at the next wedding at the venue are the same as the flowers at his and Monica's. Chandler says, "I don't know, Monica picked them out." But when they're planning the wedding, Chandler has a conversation with Monica about having lilies instead of roses at the wedding.
When Monica starts opening her wedding presents, she maniacally rips apart the wrapping on every box. Previously, she made it clear she was neat and organized to the point of ironing all wrapping paper. However, she's so excited about the wedding presents she loses control of her usual neatness compulsion.
After Rachel tells Tag she's having a baby and the scene ends, the next scene is when Monica is still opening wedding presents. When Joey comes in, you see the lights of the set and the microphone.
It was established in season 7 'The one with the engagement picture' that Chandler cannot have his photo taken without making a weird face but when he and Ross attempt to recreate the wedding photos in this episode he has no problem.
In the ballroom when Chandler and Ross are contemplating taking pictures of themselves at the next wedding, Chandler is not wearing his wedding ring.