21 details you might have missed in 'Stranger Things' season 4

"Stranger Things" season four opens with a flashback to 1979, when Dr. Brenner was still working at the Hawkins National Lab and experimenting on children. Before he heads to work, he times himself with the day's crossword puzzle in the newspaper.

One of the clues is "Shiva's wife," referring to the Hindu god. The answer Brenner puts down is "Kali" — the name of a powerful Hindu deity.

Kali is also the name of 008, the "lost sister" Eleven found in season two when she briefly ran away to Chicago.

So far Kali hasn't re-entered the story. She wasn't seen in the Hawkins National Lab massacre flashbacks because she had already escaped by the time that happened in the timeline.

Given Kali's successful escape, and this Easter egg in the fourth season's opening scene, it feels very possible that she returns into the fold somehow during either part two of season four, or in the show's fifth and final season.

Though we never see Will do a presentation, the show gives us a couple of peeks at the poster board he carried to school for his "historic hero" assignment.

Will chose Alan Turing, a man born in 1912 who died by suicide when he was 42 years old.

As the New York Times reported in a belated obituary for the historic figure, Turing was "a British mathematician who has since been acknowledged as one the most innovative and powerful thinkers of the 20th century — sometimes called the progenitor of modern computing."

But "he died as a criminal, having been convicted under Victorian laws as a homosexual and forced to endure chemical castration."

Not only is Will a part of a group of friends who love learning about computers and technology, making Turing a natural icon, but "Stranger Things" has been heavily hinting towards the possibility that Will is gay.

Actor Noah Schnapp told Insider during a recent interview that Will is "facing personal identity crisis a little bit" in this new season. Perhaps he'll finally come out to his friends by the finale.

So far in "Stranger Things," the only character who has come out as gay is Robin. She told Steve, her new platonic BFF, that she likes girls in season three.

Season four opens with Robin and Steve swapping love advice. Steve says that Robin's crush, Vickie, must like girls too because she returned the movie "Fast Times at Ridgemont High" paused at exactly "53 minutes and 5 seconds."

That's the exact moment in the movie when Phoebe Cates' character takes her bikini top off, showing her "boobies" (as Steve puts it).

Actress Phoebe Cates was referenced last season as well when Dustin told his friends that his girlfriend Suzie was "hotter than Phoebe Cates." Also in the season three finale, Steve told the video rental store manager that "Fast Times" is one of his favorite movies.

"Stranger Things" creators Matt and Ross Duffer have described the show as a love letter to the '80s. The series often includes meta-references to the sci-fi movies that inspired the story.

The phone booth graffiti says "E.T. phone home" — a line from Steven Spielberg's 1982 movie "E.T."

The first season of "Stranger Things" held many clear parallels to the seminal story about a young boy who discovers an alien and decides to help him, including the scene where the boys dressed Eleven up in a wig and helped her escape the Hawkins Lab people on their bikes.

The first "Nightmare on Elm Street" movie premiered in 1984, bringing the world a haunting horror villain named Freddy Krueger. In the movie series, Krueger haunts and kills his victims from inside their dreams.

Vecna, the new villain of "Stranger Things 4," has many parallels to Kruger, including his disfigured face and ability to infiltrate the minds of his victims.

The Duffer Brothers also took care to include an even more meta reference to "Nightmare on Elm Street" by casting the original Freddy Krueger actor (Robert Englund, now 74 years old) to play Victor Creel in the new season.

Erica is once again brought into the fold this year, making her the youngest of the kids who have had to save Hawkins again and again.

Last season, it was Dustin, Steve, and Robin who needed her help. She negotiated free ice cream in exchange for helping infiltrate the Russian base underneath Starcourt Mall. That was the moment when she delivered her memorable motto, the thrust of which she still carries in season four as she charges into the Hellfire Club wearing an American flag as a cape.

In "Star Wars: Episode V — The Empire Strikes Back," Han Solo steers the Millennium Falcon into an asteroid field in order to escape some tie fighters.

When C-3PO tries to tell him the chances of survival, Han simply replies by saying: "Never tell me the odds."

After the season three finale, where Hopper was believed to be dead, the Duffers said in an interview that Hopper's story was analogous to Han Solo's arc between "The Empire Strikes Back" and "Return of the Jedi."

Han was encased in carbonite and had to be rescued by Leia, much like Hopper being believed dead and then rescued by Joyce in "Stranger Things 4."

In the opening episode of "Stranger Things" season four, a new character named Chrissy hears and sees a spooky clock in the days leading up to her death.

Though the kids think Vecna is some new threat, the seventh episode ("The Massacre at Hawkins Lab") reveals that Vecna's real name is Henry Creel, and he was the first child to be experimented upon at Hawkins Lab — making him "001."

Knowing now that Vecna has been the puppeteer of everything in the Upside Down that's been attacking Eleven and her friends, you can see hints of his presence in earlier seasons.

The clock chime noise heard throughout season four was actually first heard in season three, episode two. The chiming began when Billy was psychically transported to the Upside Down after being possessed by the Mind Flayer. But now, with all the revelations in season four, we know the Mind Flayer was really just another tool Vecna was using to find and kill Eleven.

We saw this phone-listening station multiple times in the first season, where people recording calls made in Hawkins were identifying suspicious circumstances connected to the Upside Down.

This time around, someone is listening to the new police chief, Powell, when he calls someone for help figuring out how Chrissy died in such a gruesome manner.

In season two, when she's trying to get him un-possessed by the Mind Flayer, Joyce mentioned that Will's birthday is on March 22.

Then in the first episode of season four, the location card says it's March 21, 1986. The characters discuss that Mike is heading to California the next day — which means he arrived on Will's birthday.

But for unexplained reasons, not a single character seems to know. Is this just a slip-up in the show's details? Or is Will really being so neglected by his friends and family that they all forgot about his birthday?

In season four, episode two, we see that Lucas and the basketball team celebrated their win with a party at Benny's Diner — the first place Eleven went when she escaped Hawkins National Lab (HNL).

Back in the very first episode of "Stranger Things," Benny was killed by a woman working for Brenner. She then staged the murder to look like a death by suicide. Benny's death was one of the most tragic and direct acts of violence we saw in the show.

Seeing his diner now trashed and filled with drunk teenagers really hammers home how much has changed since that pilot episode.

Back when Lucas, Dustin, and Mike had first met Eleven (in season one, episode two), Lucas was the one positing a theory that she was a "weirdo" who had escaped "from Pennhurst."

All these years later, Pennhurst came back into the story as the asylum where Victor Creel has been living ever since his arrest for the murder of his family.

After Mike, Will, and Jonathan learn about Eleven's secret mission to regain her powers, the government officials working for Dr. Owens hand Mike a note from El.

They don't know if they can trust random government officials because they've already been so burned by corruption and cruelty within the system of the US government.

Mike literally went from trying to outrun vans full of Department of Energy employees to being trusted with a secret, highly classified note by an anonymous government employee working for a secret faction of the Pentagon.

The emotion of this scene is driven home when Mike sees the note is signed "from" instead of "love." Eleven is pulling away from Mike after his refusal to say "I love you" to her again. Now she's resolute on healing herself.

The years listed for this experience are 1985 and 1986, which covers the last two years Nancy spent with her younger friends saving the world from the Mind Flayer.

"Working with teens" is a rather cheeky way of summarizing how Nancy's real-world experience could translate to a college resume.

In the movie, the character played by Steve McQueen (Captain Virgil Hilts, aka "The Cooler King") ends up right back in the very prison he engineered an escape from, ready to plot the next attempt.

This is an early hint at the result of Hopper's escape — he made it all the way to a blissful meal of peanut butter in a church, but then was caught and hauled back to the starting point.

Now he, Joyce, Murray, and Dmitri are going to have to try and escape once again.

Ever since season two of "Stranger Things," we've theorized that there is a likely connection between Hopper's first daughter's death and the Hawkins National Lab.

One of the biggest hints that supports this theory is the recognizable stairwell (seen above) that we know is inside the HNL building.

As seen above, Hopper was in that same stairwell when he was grieving over his daughter's death in a hospital room. Does that mean Sara died inside HNL? This season we got the reveal that Hopper believes Sara got sick and died because he, Hopper, had been exposed to the chemical weapon Agent Orange. He told Dmitri he was just a teenager when he got drafted and told to work with the deadly substance.

So now Hopper believes that Sara died due to birth defects related to Agent Orange. But why would that have landed her in the secret hospital lab in Hawkins?

Insider asked Harbour back in 2017 if he could tell us more about this connection between Sara's hospital room and the HNL.

"Hmmmm [laughing] I can not," Harbour said. "But yes, it is the same location. So that's interesting. Or it's a similar location. But there's actually another thing you'll notice which is that there's a stuffed animal lion that appears in Eleven's room when he breaks into the lab and finds that room, and it also appears in Castle Byers, and it also appears on Sara's lap."

For a full breakdown of all the connections between Hopper, his daughter Sara, and Eleven, read our full report here.

We see Henry (aka "001," aka Vecna) show Eleven the entrance to a storm drain that will take her outside the boundary of HNL. This was back in 1979, the day of the massacre at the lab.

But Eleven didn't escape until 1983 — the day Will Byers disappeared and the Demogorgon was let loose in Hawkins.

Back in season one, Hopper and Mr. Clark found a piece of hospital gown fabric near the storm drain's exit. Now we have the added context to know that Eleven had been shown this escape route and remembered it all those years later when she finally managed to get free of Dr. Brenner.

Dr. Brenner used the implant to inhibit Henry's powers and track him. Or at least that's Henry's version of the story.

The term soteria is relevant to the system built in the HNL. The ethos behind it includes the preservation of residents' personal agency, surrounding them with non-medical staffing and encouraging social networks and communal tasks.

But as we've seen, the system Brenner designed didn't need 24/7 restraints or drugs in order to control and manipulate the children and Henry. The facility had a loose facade of "helping" the children learn to use their powers, but the reality included abuse, torture, and extreme emotional neglect.

The seventh episode of "Stranger Things" season four gave us a huge amount of context for Eleven's experiences both in and outside of HNL.

When Henry first uses his powers in front of Eleven, he kills several military guards. The final man is killed when Henry flicks his head to the side, snapping his neck.

In season one, Eleven used this exact same move to kill one of the HNL guards in a flashback of her time at the lab after Henry is banished to the Upside Down. So the scene (shown above) is like a reverse callback, letting us know that Eleven's killer instincts were taught by Henry.

Previous seasons of "Stranger Things" have included a lot of murkiness around the history of HNL and how Eleven was linked to the Upside Down. After seeing the first season, the only logical conclusion was that Eleven had accidentally encountered the Demogorgon while she was practicing spying on people in the Void.

But now we know that Henry Creel was the first child in Hawkins to display supernatural abilities. The source of his powers is unknown, but we know he was placed under Brenner's care against his will and then Brenner decided to try to "recreate" Henry's powers in other children.

After Henry massacred everyone inside HNL, Eleven defeated him by ripping into the fabric of space and time and sending him to the hellish Upside Down dimension.

The Henry reveal retools the understanding of the whole series because now we know that Henry was the one behind the Demogorgons, Mind Flayer, and every other supernatural creature who comes from the Upside Down.

In 1983, Eleven defeated the Demogorgon in season one (in the exact same position and style as she defeated Henry in 1979). So Henry sent the Mind Flayer next. But she defeated that creature, too. In season three, Henry once again tried using the Mind Flayer — this time assembling a physical form made from dead bodies.

And now, in season four, we finally saw the man behind the curtain. Henry is hunting teens in Hawkins, likely to try and draw Eleven out of hiding, bringing her face to face with him once again.

We'll have to wait for the final two episodes of "Stranger Things" season four to see what this epic rivalry will come to. Part two of this new season premieres on July 1.