This show is notorious and great for callbacks to old episodes. I noticed most recently in my manhood, Michael Mcdonald showed up as Mr. Cropper (he played Mike Davis in seasons 1 and 2 - "my mom pushed me down the stairs; she is fat tho - and boring") and a few minutes after his appearance they made a reference to Elliot's cold hands while examining a patient. A total callback to the episode where she was told by the Mike Davis character amongst others that she had cold hands and did rough examinations. I love the more subtle ones that cross several seasons!

Also, in my own worst enemy (sea 7 ep 1) is Marjory (always has something to say) the same actress as Perry's sister? She looks exactly like her!