Content warning: This article contains spoilers for Eternals.
Eternals is packed with tons of new characters and lots of lore from the classic Jack Kirby comic book. Like every other MCU movie and streaming series, it also has plenty of hidden details for fans to discover with repeated viewings. Some hidden details connect the movie to other MCU movies and shows, as well as link up subtle plot threads in the franchise.
Some of the best-hidden details in the movie link the Eternals to the distant past of the entire MCU, both on Earth and in the greater cosmic realm. Though Eternals is the first MCU entry in a while without a guest appearance by an existing MCU character, it does pave the way for future characters in its two post-credits scenes.
Six Singularities
Eternals opens with a great Star Wars-style opening text crawl, which gives the background on the Eternals and the Celestials. The crawl makes references to "...before the six Singularities," which is a direct reference to the six Infinity Stones.
Both Wong and The Collector have explained the Infinity Stones as existing before the universe, with each of their individual powers contributing to aspects of existence, like time and space. The crawl reframes that somewhat in order to explain the Celestials predate even the Infinity Stones, making them among the most powerful Marvel cosmic beings.
Excalibur
When the Eternals return to their ship, the Domo, in the present day, there are numerous references to historical and mythic objects. One of them is to Excalibur, the legendary sword of King Arthur. This has intriguing implications for the MCU in a number of ways. First, Dane Whitman, who comic book fans know as the Black Knight, is connected to the actual Arthur in the comics.
He is also connected to the Captain Britain Corps, of which Captain Carter from What If...? is the likely MCU representative. Finally, Excalibur is the name of the British offshoot of the X-Men. The team has been very closely linked to the multiverse from their inception right through to the current comics.
Ebony Blade
Another sword referenced in the same scene is the Ebony Blade. This hidden reference actually pays off in the movie's final post-credits scene. The Ebony Blade is the mystical weapon of the Black Knight, who Dane Whitman will eventually become in the MCU as he is in Marvel Comics.
The Ebony Blade can cut through any substance. It was created by Merlin and then handed down through each generation to a Black Knight. Dane's uncle, referenced in the movie, was a supervillain in the comics and the Black Knight before he inherited the powerful weapon.
The Monolith
One of the best-hidden details in the movie happens close to the beginning. When the Domo materializes off the coast of ancient Mesopotamia, only its nose is visible to the people on the shore. The nose of the craft is a black rectangle in the same shape as The Monolith from the classic 1968 movie 2001: A Space Odyssey.
Jack Kirby was a huge fan of many of the ideas about aliens and early man in the Stanley Kubrick movie. He also drew the Marvel Comics adaptation and a sequel monthly comic, among the most essential Jack Kirby Marvel Comics ever.
Earthquakes
When Tiamut, the Celestial gestating inside of Earth, begins to wake, he causes earthquakes all over the world. This actually pays off a great hidden detail from Avengers: Endgame. In a scene early in the movie, the surviving Avengers report various concerning developments, including mysterious earthquakes in the Atlantic Ocean.
Much of the speculation since has centered on Namor, the Sub-Mariner, whose kingdom of Atlantis is located in the Atlantic in Marvel Comics. It turns out this was actually an early hint of Tiamut and the dark fate awaiting Earth even after The Blip.
That's Superman!
One of the best references in the movie is Phastos' son, Jack, referring to Ikaris as Superman. Ikaris shares many similarities with Superman, including his ability to fly and shoot laser beams from his eyes.
Jack is clearly a comic book fan (and a Star Wars one, judging from the posters on his bedroom wall) making this a great and rare link between Marvel and DC. It's not the only DC Comics reference in the movie. Kingo's valet, Karun, gets compared to Alfred, the butler of Bruce Wayne, Batman.
WHiH News
A very hard-to-spot detail in the movie links it to many other MCU movies and related shows. WHiH is the news network playing on TV screens throughout the movie, and this network has been seen numerous times before in the MCU.
It's the network Christine Everhart, the reporter from the Iron Man movies (and now the What If..? series), works for. The network has been seen in numerous Netflix Marvel shows like The Punisher, as well as Disney+ streaming series like WandaVision and The Falcon And The Winter Soldier.
The Icarus Myth
The movie draws heavily on world mythology, with many characters directly referencing ancient legends (Makkari is Mercury, Gilgamesh is Gilgamesh). Ikaris' entire arc in the movie is in some ways a subtle reference to the Icarus myth. When Ikaris flies directly into the sun at the end of the movie, he completes the tragic journey of his mythic counterpart.
Icarus died in the myth after flying too high with wings made of wax, despite his father's warnings. Ikaris, a synthetic being, dies after trying to achieve the humanity his counterparts have and failing.
Blade
The final scene of the movie contains a great hidden detail - the off-screen voice heard warning Dane Whitman against taking up the Ebony Blade is Mahershala Ali, who will play Blade in the MCU. His voice cameo in the movie sets up a host of intriguing possibilities, making it one of the most important MCU post-credits scenes.
Blade and the Black Knight do have a connection in Marvel Comics through M:13, a covert U.K. organization dedicated to fighting the supernatural. The MCU could be setting up some form of that.
Captain America's Shield
A great hidden detail in the movie links the Eternals to the MCU's storied past. In a scene on Kingo's private jet, Captain America's original World War II shield can be seen hanging on the wall in the background. The implication is the Bollywood star purchased the shield for his collection.
Kingo may have also known Captain Rogers. Several extras in his Bollywood movie are using what seem like versions of this shield, and Kingo makes reference to knowing Thor in the past. Given his long life, it's certainly possible he and Steve Rogers once crossed paths.