1.Meredith's phone background in Season 18 is a photo of her kids under the Christmas tree – which looks a lot like the scene from Season 2 of George, Mer, and Izzie lying under the tree.
2.The outfit that Izzie wore on her first date with Alex is the same dress she wore when they first met at the intern mixer.
3.Every single episode is named after a song, except one. The first episode of Season 14 is titled "1-800-799-7233," the phone number for the National Domestic Violence Hotline.
4.And the very first song played on Episode 1 of the show, Rilo Kiley's "Portions for Foxes," also played at the end of the 300th episode, when Meredith won her own Harper Avery Award.
5.Back in Season 4, just after Burke won the Harper Avery Award and didn't give her credit, there's a scene where Cristina sings "Like a Virgin" while working in the morgue. The same song plays in the background when Burke offered Cristina a job at his hospital in Switzerland in Season 10.
6.In Season 11, we can see that the model of a spine in Callie's lab is colored in blue, pink, and purple...like the bisexual pride flag.
7.Also in Season 11, Stephanie is swiping through a dating app, and one of the guys she X's is a photo of Denny.
8.In Season 10, Derek stitches butterfly wings for Zola, which made another appearance six seasons later.
9.And in Season 16, we also see that Zola still has the lion that Derek gave her in Season 6 when she was first adopted.
10.In Season 6, Richard stopped in at a place called The Rhimes Cafe, surely named for the show's creator, Shonda Rhimes.
11.Derek once told Meredith his dying wish, but she totally ignored it.
12.According to a flier she posted looking for roommates in Season 1, Meredith was anti-Bush.
13.And Amelia is probably anti-Trump, if her answer after brain surgery is anything to go off. When asked if she knows who the current president is, she replied: "I wish I didn't."
14.MerDer's wedding Post-it Note actually came from Cristina, who wanted to give Meredith something old, new, borrowed, and blue before the City Hall ceremony.
15.Izzie's dog poster hung in the hospital for 10 whole seasons.
16.In Season 3, George pulls out a bottle of whiskey, which is clearly Knob Creek, but the prop department changed the label to read, 'Door River.' Clever!
17.Addison's return to the show in Season 18 sounded a lot like her first introduction way back in Season 1, where she greeted Meredith by saying, "You must be the woman who's been screwing my husband."
18.When Alex sends Meredith his case arraignment number after beating up DeLuca, he adds, "See you in three to five with good behavior," to the end of his email.
19.On Meredith's first day of being a resident in Season 4, she tells her 'rules' to her intern group...which are exactly the same rules that Bailey gave them in the pilot.
20.The OB-GYN who gives Sloan an ultrasound in Season 6 is the same actor who played a peds intern in Season 1.
21.In Season 3, there's a sticker encouraging people to get tested for syphilis on Alex's locker door — a sneaky throwback to the syphilis outbreak in Season 1.
22.In the Season 18 premiere, Meredith is wearing the exact same shirt she wore in the show's pilot episode.