Warning: The following contains SPOILERS for Avengers: Infinity War!
For the biggest movie so far in the biggest film franchise going, the Russo Brothers went to extreme lengths to prevent leaks and spoilers for Avengers: Infinity War. This was especially important for the movie's devastating ending, so that audiences could remain unspoiled and be properly floored when they saw it. To ensure the secrecy of the ending, even the cast wasn't told exactly what it was ahead of time. Instead, the actors were told the ending to the film right before shooting while sitting in a van, as Scarlet Witch herself, Elizabeth Olsen, explained:
I found out from the Russos exactly what was going to happen and it wasn't until we shot it on that day we learned what the ending was. They took us into a van - all of us - we were in a van with air conditioning because it was very hot and they told us how the movie was going to end and no one knew. And they were like Now we're shooting it, Go! and we were like 'How are we supposed to interpret that?'
That has to be a strange experience, being told the ending of the film while crammed in a van with all your co-stars minutes before you actually have to go film your death scenes. It sounds like it was difficult as an acting challenge too, to be told your character will turn to dust and have to figure out how to interpret that with your performance. What Elizabeth Olsen described at ACE Comic-Con (via MovieWeb) also must have been quite the visual. Think about it: all of the MCU's heroes packed like sardines in a van, listening intently as the Russo Brothers lay out what the ending is. It's almost silly, but these are the steps necessary to prevent movie leaks in the internet age. Heck, they probably swept the van for bugs first, too.
The Infinity War cast members were allowed to read the full script ahead of time if they wanted to, but to do so, they had to go into a windowless room without their cellphones and they were unable to take a copy home to memorize their lines. The actors and actresses were given bits and pieces of the script to take with them, but those pieces had fake scenes and endings just in case they fell into the wrong hands. So while the cast probably knew the broad strokes ahead of time, it sounds like what is actually occurring onscreen at the end of the film wasn't entirely clear until the Russo Brothers laid it out and explained what was happening to their characters once Thanos snapped his fingers.
Now not all of the cast members were kept in the dark about their character's fates in Infinity War. Loki actor Tom Hiddleston also revealed at ACE Comic-Con (via Comicbook.com) that he actually found out that his character would run out of tricks and meet his end prior to filming Thor: Ragnarok, as he explained:
So, I've known about that scene for two years. I met with Marvel in May 2016, and they were actually telling me the story of Ragnarok with concept art and images. The Russos came in, and I introduced myself. So, all four of us sat down, and they said this is how Infinity War begins,
I guess given how little Loki is in the film, it was probably kind of hard to tell him his role in the film without revealing his death. Knowing his tragic fate actually influenced how Tom Hiddleston played the character in Ragnarok, and by knowing what was coming, he was able to help Loki become an 'Odinson' again before he met his end.
The Marvel secrecy machine rolls on as we head into next year's Avengers 4. That final film of Phase 3 carries with it not only the question of who will die, but also who will be resurrected somehow to fight again and what the MCU will look like as it enters Phase 4. If the cast were all crammed in a hot van to learn the end of Infinity War, I can't imagine what they must have went through to learn the conclusion of this next chapter.
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