Fans spent an entire year following Avengers: Infinity War wondering how their heroes would take down Thanos (Josh Brolin) and restore balance to the Marvel Cinematic Universe. And in the two weeks since Endgame has hit theaters, there have been even more theories that explain how it all went down.

Among the lingering questions: Why didn't the Avengers use the Infinity Stones to bring back Tony Stark (Robert Downey Jr.)? Was that a Skrull posing as a teacher at Peter Parker's (Tom Holland) school? And what really happened in that final scene with Captain America (Chris Evans)?

Endgame screenwriters Christopher Markus and Stephen McFeely tackled all of these burning questions and more during a visit to Heat Vision Breakdown , a weekly genre video series from The Hollywood Reporter.

Perhaps the most hotly debated Endgame plot point is the fate of Captain America, who travels back in time to live out his life with Peggy Carter (Hayley Atwell). 2014's Captain America: The Winter Soldier established that Peggy had a husband and two kids, and some fans have theorized that Steve Rogers secretly was this husband all along. Others have stated that Steve created an alternate timeline when he went back to live with Peggy, and somehow got back to the mainline MCU as an old man.

Markus and McFeely accept that different people will have different viewpoints on this topic. But, in their minds, Steve was Peggy's husband all along.

"It was always our intention that he was the father of those two children. But again, there are time travel loopholes for that," said McFeely.

Added Markus: "It does introduce the idea that there are two children who have somewhat super soldier DNA."

Read on for more burning fan theories that the duo tackled.

Was there really only one way to defeat Thanos?

In Infinity War, Doctor Strange (Benedict Cumberbatch) willingly gives up the Time Stone in order to spare Tony Stark's life, telling him there was only one future in 14 million in which the Avengers win. Fans have theorized that there were in fact multiple ways the team could have beaten Thanos, but Doctor Strange picked the one scenario in which the Infinity Stones would also be destroyed, ensuring they could not be used for evil again.

Verdict: Not true.

"The only way this works is if Tony dies. If you go back and watch Infinity War, when [Strange] says 'one,' Benedict … is just choked on emotion. Now that you know the end, go back and watch that moment. He means, 'You're going to have to die, Tony.'"

Could the Avengers have brought Tony Stark back to life using the Infinity Gauntlet?

Endgame saw half of all life in the universe return, thanks to the Hulk (Mark Ruffalo) using the Infinity Gauntlet. Couldn't he have done the same after Tony's death to bring him back?

Verdict: Nope.

"The Gauntlet, as of yet, has not brought back anybody to life that wasn't removed by the Gauntlet. Tony was physically killed," said Marcus.

The counterexample would be Vision (Paul Bettany), who was revived briefly in Infinity War by Thanos after Scarlet Witch (Elizabeth Olsen) killed him. But the writers note Vision was brought back via the Time Stone, which saw Thanos rewind time a few moments to before Vision's death. That's a little different than bringing back someone who had already died.

Bottom line: If you were snapped, you can come back. If you died some other way, as far as we know, you can't.

Could Steve Rogers wield the Infinity Gauntlet?

Only Thanos and the Hulk have used the Gauntlet and survived. But there's a famous moment in Infinity War in which Steve Rogers briefly holds Thanos at bay, pushing back at the villain's gloved hand.

Fans have theorized the Gauntlet was responding to Steve's strength of will, which would suggest Cap was strong enough to use the gauntlet.

Verdict: Not true.

"I think Steve would be toast," said Markus. "I think in that moment, Thanos is impressed by Steve's will. He's like, 'I can't believe this guy who apparently has no powers is trying this.' He's almost like, 'Really? Really?'"

Did Steve Rogers offer Bucky the mantle of Captain America?

Steve's best friend Bucky (Sebastian Stan) knew that Cap planned to live his life in the past, telling Steve he'll miss him before the trip. Steve ultimately reappears as an old man, and offers the Captain America shield (and title) to his other close friend, Sam Wilson (Anthony Mackie). Fans have theorized that Steve initially offered Bucky the Captain America title in an offscreen conversation, but Bucky rejected it.

Verdict: Partially true.

Yes, the two had a conversation before Steve went back in time. But no, Steve never offered the mantle to Bucky, said the screenwriters.

"That's not our intent, no. It's just honoring their relationship," said McFeely. "Steve, clearly, before he stepped on that platform … told Bucky what he was going to do. Whether he knew he was going to appear on that bench, I don't think so. Why would Bucky say, 'I'm going to miss you pal,' if it was only going to be five seconds?"

Was there a Namor reference in Endgame?

THR's Richard Newby argued in October that Namor should be the villain of Black Panther 2. In Endgame, Okoye (Danai Gurira) reports there have been undersea earthquakes. That's totally a Namor Easter egg, right?

Verdict: Not true.

"I wish we were that smart," said Markus.

Is Ben Mendelsohn's Captain Marvel character Talos in the background of Peter Parker's school?

Some fans are convinced they can spot a Skrull (in human form) at Peter's school near the end of the film. Is this a hint at the famous Secret Invasion comic book storyline, in which Skrulls posing as humans invaded all segments of society?

Verdict: Not true.

The big problem with this theory? The screenwriters are not aware of Mendelsohn being in the movie, so he almost certainly is not in it.

"There are things people have told me about these movies, which we have worked on for nearly five years, that I've never seen, so I should probably watch it again," said Markus.

Did the Hulk or Tony's snaps in Endgame release radiation that could create mutants?

Monday's trailer for Spider-Man: Far From Home establishes that one of the Endgame snaps tore a hole in the MCU, apparently opening it up to new dimensions. If it can do that, could it also help introduce mutants into the MCU?

Verdict: Who knows, but probably not.

Markus and McFeely say they were unaware of the idea that a snap tore a whole in reality until they watched the Spider-Man: Far From Home trailer on Monday. So they aren't convinced it could also help explain future mutants.

"Anything is possible, but I don't know whether you'd need that. Genetic mutation is genetic mutation. It just happens. Maybe they are already out there," said Markus.

With Disney's recent acquisition of 21st Century Fox, the X-Men and Fantastic Four are available to Marvel Studios head Kevin Feige for the first time, and fans have been theorizing about how those characters could be folded into the MCU.

"I do think that whenever Kevin decides to do X-Men or Fantastic Four, it won't be how you think it's going to happen," said McFeely. "I think he's going to have a real clever version of it."

A few more questions that aren't really fan theories ...

How did that all-female shot come about?

Endgame featured a crowd-pleasing shot in which the women of the MCU gathered, with the characters involved including Captain Marvel (Brie Larson), Scarlet Witch, Valkyrie (Tessa Thompson), Okoye, Mantis (Pom Klementieff), Shuri (Letitia Wright), the Wasp (Evangeline Lilly), Gamora (Zoe Saldana), Nebula (Karen Gillan) and Pepper Potts (Gwyneth Paltrow).

"We certainly thought long and hard about it. I remember on set that day when we did it, every woman in the crew came down because they were incredibly excited to see it. It was a big moment and we took pictures of everybody," said McFeely.

Markus called it a celebration of these characters, with McFeely adding: "We asked ourselves, have we earned it? And occasionally in the edit we'd say 'Should we take it out?' And everyone said, 'I like it. I like it.' "

Was there a version of an alternate Captain America 3 before it became Civil War?

Downey was not always guaranteed to star in what would become 2016's Captain America: Civil War, and Markus and McFeely put together a partial story without Iron Man.

"There were outlines where we had the Zemo [Daniel Brühl] plotline based around Bucky. We had that whole structure. But it wasn't so much about pitting Steve and Tony together. When Civil War rose to the surface, it fit in really nicely into that," said Markus.

Added McFeely: "It wasn't a great enough A-plot. It became an excellent B-plot."

And finally …

Who puts mayonnaise on hotdogs?!

One of the standout moments from Endgame came when Hawkeye's wife, Laura Barton (Linda Cardellini), asked if her family wanted mayonnaise on their hotdogs. Endgame directors Joe and Anthony Russo recently told MTV's Josh Horowitz they presumed Markus and McFeely came up with that line, because they'd never heard of anyone putting mayo on hotdogs.

Unfortunately, not even Markus and McFeely are sure where the line came from.

What follows is a transcript of the exchange in which they were asked them about it …

THR: What's the real story on mayonnaise on hotdogs? Do you guys put mayo on hotdogs?

Markus: No. It's in the script, I think.

McFeely. No [it's not in the script].

Markus: I believe it is.

McFeely: Is it?

Markus: Yeah, who puts mayo on a hotdog? I think that is in the script.

McFeely: No one I know puts mayonnaise on a hotdog.

Markus: That's why the question is in the movie.

McFeely: Huh. I don't know why that happened.

THR: You've never put mayonnaise on a hotdog?

McFeely: No! It's disgusting. For psychopaths! Why would you do that?

Markus: I could see it working.

THR: I feel like you have put mayonnaise on a hotdog.

Markus: I can't recall having done it, but sometimes you go to Europe and strange things happen.

***

For more from the Avengers: Endgame screenwriters, check out the second part of their interview, where they discuss the 60-page document they gave to Marvel before writing Infinity War and reveal it included words that will mean something to comic book fans: House of M.