Marvel Cinematic Universe: Definitive Guide To Easter Eggs, In-Jokes And Foreshadowing
The Avengers
11. Lokis Staff Is An Infinity Stone
While the gang argue amongst themselves, the camera spins around to focus on Loki's sceptre, revealing it's the source of all the team's conflict. At the time it was assumed (as stated by Nick Fury) that the gem was controlled by the Tesseract, but it's since been confirmed by Kevin Feige as an Infinity Stone. And, given what it's seen doing here, it's clearly the Mind Stone.
10. Banner Tells The Story Of The Alternate Opening
Banner's monologue about trying to kill himself, only for his angry alter ego to prevent it, may be familiar to serious MCU fans; it's the canonisation of the event seen in the alternate opening of The Incredible Hulk (which also featured an early appearance from a frozen Captain America).
9. Banner Sees The Tesseract
Not quite an Easter egg, but a quick shot that explains away what is often stated as a plot hole in the movie; just before Hawkeye's arrow explodes, the computer locks in on the Tesseract's energy signature in New York, seen only by Banner. That's how he knew to head to NYC after falling all that height.