What is the meaning of this joke??

The joke is : "Hello Nurse" said a rabbi, phoning me at our hospital nurses station. "I got a call that a patient wanted to see me, but I'm not sure which one it was." Clueless myself, I took a wild stab, and walked into a room, woke the patient and asked, "Did you request a rabbi?" "No, she replied sleepily, "I ordered a chef's salad".