Avengers: Infinity War is the culmination of 10 years of superhero movies. The film builds off 18 previous movies, with hidden references crammed throughout its runtime. The Marvel Cinematic Universe is known for putting Easter eggs in every movie, from comic book and pop culture allusions to callbacks within the series itself. Not only do these little bonuses make the films more fun, but they can also sometimes lead to wild speculation about the direction of the series. They aren't all just goofy jokes.
This extreme attention to detail makes it almost impossible to keep up with every little reference, and even the most astute viewers are bound to find things they missed in Avengers: Infinity War. Obviously, the film makes extensive allusions to the comic books that inspired the film, but not every Avengers: Infinity War Easter egg comes from the comics. While calling Drax Mr. Clean is a reference almost everybody would get, there are likely a few others that went over your head.
When Cull Obsidian and Ebony Maw arrive in New York City to take down Tony Stark, Wong, and Doctor Strange, Cull Obsidian is sporting a familiar accessory. Eagled-eyed viewers noted the material hanging from his belt looks a lot like Carol Danvers's - AKA Captain Marvel's - suit.
Knowing Marvel Studios, this can't be a coincidence. Some speculate this means Cull has fought with Captain Marvel in the past. Others think he may have even killed her. There is some connection there, and hopefully, 2019's Captain Marvel will specify what.
At the end of Guardians of the Galaxy Vol. 2, Yondu Udonta gives Star-Lord a Zune music player that comes pre-packaged with a whopping 300 songs. This is important because Star-Lord realizes that Udonta is the closest thing he's ever had to a father.
When we first see the Guardians in Infinity War, they're listening to the song "The Rubberband Man" by The Spinners. It's safe to assume this is playing off of Star-Lord's fancy new Zune, which means that it was one of Udonta's favorite songs. This is interesting because the story goes that "The Rubberband Man" was written by producer Thom Bell to help his son with his weight-related self-esteem issues. It also makes the scene in which the crew makes fun of Star-Lord for his perceived weight gain somewhat ironic.
Avengers: Infinity War isn't the only thing the Russo brothers have directed. They also directed Captain America: The Winter Soldier, Captain America: Civil War, and several episodes of the hilarious sitcom Arrested Development. As such, the Russo brothers love putting odd references to Arrested Development in their Marvel films. For example, the Bluth family's stair car made an appearance in Civil War. In Infinity War? They crammed Tobias Fünke into a glass tube.
As the Guardians sneak up on Thanos interrogating the Collector, Gamora walks past a glass cylinder that appears to contain a mustachioed blue man in jean shorts. It doesn't look like Arrested actor David Cross in there, but the reference is clear. The Collector has managed to acquire one of the only known "Never-Nudes" in the entire universe.
Most MCU fans are aware of the Wakandan war cry, "Wakanda Forever!" What they may not have noticed is Black Panther's cry of "Yibambe" in Infinity War. It isn't a vague, African-sounding word producers came up with for the film - it's actually from the Xhosa language spoken by some 20 million Africans.
It means "hold," and is a call to rally the troops and stand together in the face of overwhelming odds. On some level, this probably demonstrates Wakanda's newfound willingness to interact with and borrow from other African nations.