Sean Astin (Bob Newby) actually returned to the Atlanta set to shoot his brief scene with Winona Ryder (Joyce Byers). In an interview with Entertainment Weekly, Stranger Things co-creator Matt Duffer said: "He flew in for one day to shoot that scene with Winona. We had talked about, like, we can just flash back to them dancing or whatever, but we really thought it would hit a little bit harder if it was a new moment between the two of them. That was hard, too, just having Sean back for one day. Winona and Sean are especially close. It just made everybody miss him that much more."
The first time we see El's (Millie Bobby Brown) bedroom, the camera pans across her walls and we can see the mask that she wore when she was with Kali's (Linnea Berthelsen) gang.
When Hopper is talking to Mike and Eleven, he tells Mike that Mike needs to get home and says, "It's your grandma." The scene cuts quickly and abruptly after the word "grandma" to Hopper and Mike getting in Hopper's truck. This is because at each take of the scene, David Harbour would burst out laughing each time he said, "It's your grandma." It would appear that the Duffer Brothers decided to salvage the scene by cutting the second Harbour was able to say "grandma" without laughing.
The score that plays when Dustin's (Gaten Matarazzo) toys begin moving around "by themselves" is from Killer Klowns from Outer Space (1988) by John Massari.
Dustin (Gaten Matarazzo) names his portable long-range radio tower Cerebro. In Marvel Comics' X-Men comic books, Cerebro is a device used by Prof. Charles Xavier to amplify his telepathic powers, allowing him to detect fellow mutants around the world.