1. Noah Schnapp (Will Byers) initially auditioned for the role of Mike.
2. 246 young actors actually auditioned for the role of Eleven.
3. Mike was originally conceived with a large birthmark on his face.
4. Meanwhile, Dustin was originally written as wearing glasses.
5. When the Duffers called Caleb McLaughlin to tell him he got the part of Lucas, they actually pretended it was bad news just to mess with him.
6. Steve was supposed to be killed off in Season 1.
7. Eleven's iconic pink dress was based on the style of Polly Flinders brand dresses that were popular in the '70s.
8. The boys' famous walkie talkies were actually found at a flea market in Long Beach, CA.
9. And each of their BMX bikes were tailored to fit their characters.
10. When the show first aired, David Harbour (Chief Hopper) was convinced the show was going to be a failure because he didn't see any subway ads for it in NY, where he lives.
11. Shannon Purser, who played Barb, taped her first audition for the show in her parents' basement.
12. Every single bulb in Joyce's iconic Christmas light setup was a practical effect and could actually be turned on and off as needed.
13. For the infamous van-flying-through-the-air scene, they actually, practically, fired a van into the air.
14. Millie Bobby Brown wore an earpiece when she was submerged in the sensory-deprivation tank.
15. There are actually FIVE "stages" to the Demogorgon's morphology — Pollywog, Frogogorgon, Catogorgon, Demodog, and Demogorgon.
16. Bob was originally supposed to die much earlier in Season 2, in Episode 4 (rather than the finale).
17. There are a lot of secrets to Hopper's backstory with his daughter — and we may never learn them all.
18. Although it's a part of the show, we may never get a deeper look at MKUltra in future seasons.
19. The Duffers were actually intimidated by the idea of directing Winona Ryder.
20. Dacre Montgomery's infamous audition tape (shirtless '80s dancing!!) for the role of Billy caught the filmmakers totally off guard.
View this video on YouTube
The show's producers "knew immediately they had found the right actor for the role."
21. Sadie Sink does not like horror movies — which is funny when you consider Max wears a Michael Myers mask for Halloween.
22. The Duffers specifically referenced the shark in Jaws when giving direction to actor Mark Steger, who played the Demogorgon in Season 1.
Steger explained, "I tried to make it as creepy as possible, just doing really subtle moves."
23. 27 individual motors are required to create the effect of the Demogorgon's face opening and closing.
24. The arcade in Season 2 was built inside a former laundromat in Georgia.
25. Many of the scenes inside Hawkins Lab were shot at the former Georgia Mental Health Institute — a former psychiatric hospital.
26. If you feel like the show looked particular "orange" in Season 1 — especially for it being set in 1983 — that's because they wanted it to look fall-colored.
27. The Duffer brothers came up with the initial idea of Stranger Things way back in the fall of 2013.
28. And, in their infamous look book that they used to pitch the show, the Duffer's design of the Demogorgon referenced the works of Guillermo del Toro, Clive Barker, and H.R. Giger.
29. The first scene the Duffers wrote was actually the Dungeons & Dragons scene.
30. For the upcoming Season 3, the crew actually took over parts of two floors in an existing shopping center to make Hawkin's ~new~ Starcourt Mall.
31. And, following suit of the past two seasons, Season 3 will take place roughly one year later in 1985 — but in the summer (rather than the fall).
Facts for this post have been sourced from Stranger Things: Worlds Turned Upside Down: The Official Behind-the-Scenes Companion.
And if you're interested in reading even MORE behind-the-scenes facts you can get the book for $16.50 on Amazon.