After Rachel comes screaming out of Monica's bedroom, she's wearing an open toed sandal type shoe. Seconds later, when the she goes to the door to answer it, she's wearing a completely different pair of dress type shoes.
At the beginning Rachel is wearing "Pilgrim" type pumps. When Monica chases her out of the bedroom Rachel is wearing mule-type sandals and when Ross and Joey arrive she's back to wearing the pumps.
Phoebe's starfish barrettes change position in her hair between shots.
While searching for Emily, Ross dials a wrong British number that begins 011-44-74. The 011 is the code to dial an international call from North America, and the 44 is the code for Great Britain, but no British phone number would have continued with "74" until November 2009, when the code was issued.