The teaser depicts Eleven and a woman, with close-ups of their mouths, and interspersed with images of Hawkins National Laboratory, the sinister Dr. Martin Brenner, who led these experiments, and shots of sunflowers, rainbows, and other young women, which could further hint at Eleven's mother and the rest of the test subjects.
The number 450 also repeatedly appears, as well as newspaper clips suggest that Brenner and the MKUltra program may be exposed. As those images flash, the woman mutters "sunflower, three to the right, four to the left, rainbow, 450," and she experiences nose bleeds similar to Eleven's.
While it remains to be seen whether this woman is actually Eleven's mother Terry, this promo does hint that fans will be given insight into the past as to how and why Eleven was chosen for experimentation. At the end of the first season, Eleven disappeared after defeating the Demogorgon and helping to save Will Byers, but with the Upside Down set to encroach on reality once more, she is expected to return to fight alongside her friends against other monsters from this dark dimension.
Debuting Oct. 27 on Netflix, the second season of Stranger Things stars Winona Ryder, David Harbour, Finn Wolfhard, Millie Bobby Brown, Gaten Matarazzo, Caleb McLaughlin, Natalia Dyer, Charlie Heaton, Cara Buono, Matthew Modine, Noah Schnapp, Joe Keery, Sadie Sink and Dacre Montgomery.