If you've binged( ) and thought Eleven (Millie Bobby Brown) looked slightly different in some scenes, you have good reason.
Minor spoiler ahead -- the latest season sees Eleven return, via flashback, to her old stomping ground in Hawkins Lab. However, this time she explores lost memories of what happened there, including her interactions with a certain lab orderly named "Peter Ballard" (we later find out this name is a massive misdirection). In order to film these scenes, a stand-in was required for Millie Bobby Brown, given the age difference.
Eleven's stand-in is played by Martie Blair. The unfortunate byproduct of using facial mapping technology is that Eleven occasionally gives off uncanny valley vibes. Not to mention the occasional confusion over old Eleven and young Eleven's interactions with the flashback -- sometimes they're both included in the scene. On top of that, sometimes old footage of Bobby Brown's original Eleven scenes appears to be used, further emphasizing the uncanny valley moments when they come.
Regardless, that doesn't take away from Blair's performance. The young actor shared behind-the-scenes pictures of her time working on the show, including her counterpart providing extra direction.
And here's Blair with Jamie Campbell Bower, another new addition to season 4's cast.
"Thank you @Milliestopshate for being such an inspiration to me, when I showed up on set, you came right up to me. You made me feel so comfortable and welcomed. Thanks for spending time with me and helping me make my scenes AWESOME!!!," Blair tweeted, with a photo of her and Bobby Brown in front of a smashed mirror inside Hawkins Lab.
The Stranger Things writers' account tweeted a behind-the-scenes look at Bobby Brown providing Blair with direction.