1.The radio channel Hop uses to communicate with Eleven with is channel 11.
2.The secret knock Hop and Eleven use spells out "us" in Morse Code.
3.Mrs. Wheeler's romance novel cover was apparently photoshopped to look like Billy.
4.Bob notices "Sattler's quarry" when he's looking at Will's drawings — which is the same location where Will's (fake) body was found in Season 1.
5.Speaking of Season 1, the scene where the kids are playing Dungeons & Dragons in the very first episode lines up creepily perfect with the Demogorgon scene in Episode 8.
6.And in the first episode of Season 1, Joyce does this very subtle, but kinda funny (and also very sweet) thing where she reaches for Will's shoulder.
7.In Season 1, Lucas and Dustin (kinda) joke about how they think Eleven might be an escaped mental patient, like the Halloween character Michael Myers. Ironically, in Season 2, Lucas's and Dustin's crush Max is actually dressed as Michael Myers.
8.When Mike has to pick out toys for the yard sale in Season 2 he lingers on a dinosaur — which is one of the toys he first showed Eleven back in Season 1.
9.Eleven tells time "weird" because it's just the way Mike taught her back in Season 1.
10.The word "evil" is clearly written on the bathroom stall when Dustin finally finds Dart.
11.One of Kali's gang members is named Funshine, as in the Care Bear Funshine Bear — which is the exact Ben Cooper Halloween mask he wears, too.
12.The story of "Baby Fae's Baboon Heart" on the cover of Hawkins' newspaper in Season 2, Episode 1 was a real news headline in 1984.
13.Speaking of this Hawkins newspaper, this is the same edition Lucas's dad is reading — a few days later, mind you — in Episode 5.
14.The book Hop reads to Eleven in Season 2 is Anne of Green Gables, which is the same book he read to his daughter Sara in Season 1.
15.Eleven sees a trailer for the movie The Terminator in Episode 2, which is the same movie that's playing at the movie theater in downtown Hawkins.
16.The song Hop chooses for him and Eleven to clean to is called "You Don't Mess Around With Jim," which is both cheeky and adorable.
17.And finally, the "Boy Who Came Back To Life" article reads VERY differently in Season 2 than it did in Season 1.