2.Speaking of music, shortly after Burke leaves Cristina, she sings "Like a Virgin" in the morgue — in Season 10, when Burke offers Cristina a job at his hospital in Switzerland, a cover of "Like a Virgin" plays in the background.
3.The first song played in the series, "Portions For Foxes," plays again at the end of the 300th episode after Meredith wins a Harper Avery Award — a perfect full-circle homage.
4.When Meredith tells Cristina she's getting married, Cristina gives her a grocery list written on Post-It Notes and her favorite pen — Meredith and Derek use the Post-It Notes and pen when writing their vows.
5.In the pilot, George asks, "We're going to survive this, right?" foreshadowing that he is the only member of the original interns to die.
6.Also, the original interns' names — Meredith, Alex, George, Izzie, and Cristina — spell out "magic."
7.In Season 2, Izzie tries to give away their dog, Doc, by hanging flyers in the hospital — in Season 12, you can see that one of the posters is still hanging.
8.In Season 5, Lexie tells Mark that when she's hurt, she likes to have her hair stroked — in Season 8, when Lexie is dying, Mark does just that.
9.In Season 6, Richard is eating at a café called The Rhimes Café — a nod to series creator Shonda Rhimes.
10.In the pilot, Meredith corrects Bailey when she forgets to list one of her five rules — in Season 4, Lexie does the same thing to Cristina.
11.Following Denny's death in Season 2, Izzie wears the sweater she knitted for him while she's grieving.
12.When Richard is comforting Arizona in her car, you can spot a parking permit for people with disabilities on Arizona's dashboard — a small detail since Arizona lost her leg in Season 8.
13.In Season 1, Derek tells Meredith that if he was ever in a coma, he would want all of his sisters to be there — in Season 11 when Derek dies, Amelia is pissed at Meredith because she wasn't there to say goodbye.
14.After Derek's death, Meredith decides to wear his ferry boat scrub cap from then on.
15.In Season 12, Meredith takes a flight using Sky Trip Express — this is the same company that owned the plane that crashed in Season 8.
16.The OR schedule will sometimes feature the names of crew members, like this board in Season 13.
17.In Season 6, April is briefly fired after failing to check a patient for signs of smoke inhalation — in Season 13, she makes sure none of her interns make the same mistake.
18.When Cristina learns that Burke has won a Harper Avery Award, the newspaper clipping is written by Tony Phelan — he was a writer and producer on the show.