Warning: Spoilers for Avengers: Endgame ahead.

In less than two weeks, Avengers: Endgame has already become the second highest-grossing movie ever (watch out, Avatar). The blockbuster flick, which concluded the 22-film long Infinity Saga, was jam-packed with intensity, exciting action scenes, high emotion, and a ton of subtle Easter eggs you might have missed.

1. Departure déjà vu

One of the most interesting Easter eggs came near the end of Endgame, when Steve Rogers prepared to return to the past and experience life with Peggy Carter again. Before entering the Quantum Realm, Steve says goodbye to Bucky, telling him, "Don't do anything stupid until I get back," a line that was first used by Bucky in Captain America: The First Avenger. (Bucky's reply to this—"How can I? You're taking all the stupid with you"—is how Steve had originally responded.)

2. X-Men acknowledgment

Now that Disney and Fox are one entity, comic book movie fans are just waiting for the X-Men to meet the Avengers—and even Marvel Studios president Kevin Feige has said that "it only makes sense" for these two worlds to come together. Just how closely their worlds will intertwine is yet to be announced, but a blink-and-you'll-miss-it scene in Endgame gave us our first confirmation that the two superhero groups do indeed exist in the same universe. In the scene where Scott Lang visits the Vanished Memorial, the name Roberto da Costa appears on the list. Why does this matter? Because da Costa is one of the New Mutants, who is better known as Sunspot.

3. Black Widow's ballet shoes

One quiet callback that likely went unnoticed by many viewers was a pair of worn ballet shoes by Natasha's desk, a reference to the dancing she did at the Red Room, when she was training to become Black Widow.

4. Harley's return

In 2013's Iron Man 3, Tony teamed up with a 10-year-old named Harley Keener, who sort of stole the movie. Ty Simpkins, the actor who played Harley, can be seen again briefly in Endgame, in the funeral scene.

5. Joe Russo’s groundbreaking cameo

Endgame’s directors, brothers Anthony and Joe Russo, have made cameos in their own films in the past, but Joe's appearance in Endgame was a particularly important one. During a group therapy session, Russo appears on-screen to discuss the traumatic effects of Thanos’s snap. While it's fun because it's incredibly meta, his reference to his husband makes Russo's character the first openly gay character in MCU history.

6. Thanos’s Infinity Gauntlet Nod

Thanos's armor is a nod to Infinity Gauntlet in Avengers: Endgame (2019)Marvel Studios

Endgame did not wait to deliver an incredibly shocking moment for moviegoers: Shortly into the film, the Avengers travel through space to find Thanos at a farm and he’s quickly killed after Thor chops off his head. But before the Mad Titan’s decapitation, there’s a shot of his armor being used as a scarecrow—which is an image that has been seen in the Infinity Gauntlet comic series.

7. Iron Man's armor tribute

Endgame broke a ton of new ground in MCU history, but one major distinction it had from its 21 predecessors was the lack of any post-credits scenes. Instead, the only thing fans were given was a pounding, clinking sound. For those with exceptional memory and hearing, those noises may have sounded familiar. If they did, it's because they were the same sounds you heard in the original Iron Man, when Tony Stark constructed his first first Iron Man suit in Afghanistan.