The One with Two Parts: Part 2 - S1-E17
Corrected entry: When George Clooney answers the phone (while Monica and Rachel are pretending to be each other), he starts handing the phone to Rachel, saying "Rachel, it's your dad", but should be passing it to Monica (as he thinks her name's Rachel). The angle then changes, and now he's handing it to Monica.
The One with Two Parts: Part 2 - S1-E17
Corrected entry: When Monica is filling out Rachel's medical information, she has to change the name on the form so Rachel can use her insurance. You can see that she has a pencil in her hand. However, she goes up to the desk to get a new form. It makes no sense that she would arouse suspicion when all she had to do was erase Rachel's name and put hers.
Correction: Insurance forms often have multiple carbon copies. Even a pencil will leave a carbon impression on the other pages from the pressure of the tip. If there were no carbons used, the pencil point still leaves an impression on the top copy, even when erased. Monica is also perfectionist, she did not want there to be any revealing inconsistencies on the form.
Correction: In the first shot it is not clear that Noah Wyle's head is in the way. If George Clooney passed the phone straight to Monica then he would hit him. In the next shot it is clear that he passes the phone while avoiding him which is why he appears initially to be passing it to Rachel.
tw_stuart