Rachel wouldn't need a head covering as a single Jewish woman. Only as a married woman must ones hair be completely covered
The premise for this episode came from a true life encounter Larry David and Michael E Perry had in a deli. Two Haredi Jewish men were eating lunch across from Perry and David. Perry, a gentile, bet David, a Jew, he could understand more Hebrew than David. While eves dropping for 30 minutes on the conversation, Perry and David called it a draw with neither understanding a word the Haredi Jews spoke.
Both Mekhi Phifer and James Pickens Jr. were portraying doctors on television at the time. Phifer was playing Dr. Gregory Pratt on ER and Pickens had just assumed the role of Dr. Richard Webber on Grey's Anatomy.