When Sandy pulls out the puppets, Mr Wigglemuch is on his left hand and the grumpist on the right. Then the shot goes to Ross and when is goes back to Sandy, the puppets are switched and Sandy couldn't have switch both puppets that fast.
When Joey is trying to figure out what Ross's thing is, he pulls his right hand up to his chin thinking. At the end of the shot, it's his left hand on his face.
When David and Mike are in Phoebe's apartment and talking about going to Minsk, Mike's arms are folded when shot from behind but at his side when shot from the front.
When Ross says that he made up a joke and told it to Chandler, he is holding a slice of pizza with a large slice of pepperoni on it. When the camera changes and he says, "Yep, that's my thing", the pepperoni disappears.
When Ross and Rachel enter their kitchen to discuss firing the male nanny, the swinging kitchen door is open behind Rachel. But from the wide shots in the living room, the door is closed both before they enter and as they're exiting.
It is obvious that Sandy is not actually playing the recorder - the fingering does not match the melody.
As Chandler is leaving the apartment, after Monica says, "I love you," when he says, "I love you too," his lips aren't moving.
Ross says that Emma is 2 months old, and in the previous episode they say it's Halloween (so birth date in late August, which more or less correlates with it being very hot at Rachel's due date). However, in season 8, while Rachel is pregnant and they have the Thanksgiving dinner, she is about 4 months pregnant (so birth in April/May), meaning that Emma should be about 6-7 months old by the time of Halloween/Thanksgiving.
However, in the 7th season, when Monica buys her wedding dress, she says that her wedding is on May 15th. We know that Rachel gets pregnant about 1 month before the wedding (birth in January). Therefore, she could only be 2 months old in early November if Ross's statement in this episode is correct and all other dates are incorrect.
When Chandler is mocking a co-worker of Monica's, he says that he can be emailed at "www...". Email addresses don't start with "www".