Back in May, I traveled with a group of journalists to the London set of "Avengers: Age of Ultron." Now that the first trailer is out and the general public knows a bit more about the film, I'm able to talk about some of that trip.

Also, I can say that what I saw and heard was ridiculously cool.

Beyond that, I can tell you that I watched two scenes being filmed (one of which I describe here) and spoke with most of the cast. What you'll read below is based on two of the roundtable interviews I and other journalists did with actors Mark Ruffalo (Bruce Banner) and Robert Downey, Jr. (Tony Stark), and one of the scenes we watched.

So without further ado, this is some of what I learned on the set of "Avengers: Age of Ultron."

1. Ultron is screwing with the Internet.

Not cool, right? I never learned what exactly the villain was up to on the World Wide Web, but it was enough to cause Tony some concern.

2. Tony has to go looking for clues.

Whatever Ultron is up to, it requires Tony to head into a central Internet hub, what amounts on set to a dark room filled with enormous servers.

3. He brings a "magnet."

Not a literal one. It's a metaphor. While he's searching for Ultron and snooping out nuclear launch codes for fun, Tony asks one of the workers how you find a needle in the world's largest haystack. Get it now? I don't know what the magnet is, but it made looking for Ultron's presence that much easier.

4. The Black Widow-Hulk relationship isn't just fan fiction.

This tender moment from the trailer does mean big things for your tumblr and the actual film. Ruffalo, who has previously said more to journalists than Marvel would like, acknowledged a budding relationship, but wouldn’t elaborate. He was being extra careful this time not to divulge too much. "There’s a really important relationship," he said before adding, "I was just happy that I was in the movie at all."

5. The Hulk and Banner have a "detente"... for now.

That's Ruffalo's word for it, at least. From the sounds of it, Banner's "secret" from "The Avengers" remains the key to keeping the Other Guy somewhat on the leash. "I’m always angry," Ruffalo said. "Therefore I have some control over it." That's not to say the Hulk is tamed, though. "But like anger, when you think you have control over it, you absolutely don’t," he added.

6. Banner isn't sure if that control is a fantasy.

Thanks to the Scarlet Witch's (new cast-member Elizabeth Olsen) head game, most of the team will come face to face with their worst fears. For Banner, it's that this pseudo-family that he's part of is all an illusion, something that the Other Guy will take away from him at any moment, leaving him all alone again. He's afraid he belongs that way.

7. The Science Bros are roomies now.

On top of sharing a lab with Stark in the newly christened Avengers Tower, Banner has an apartment all to himself theres.

8. Want a preview of the Hulkbuster fight? You might want to watch this.

When asked about the tussle, Ruffalo compared it to the Paul Newman classic. Also: "[The fight] has a surprise, a little twist to it as well."

9. The new Hulk motion-capture is impressive.

Aside from playing this beardy gentleman, mo-cap wizard Andy Serkis consulted on Ruffalo's Hulk performance, which is more involved than last time. "I see the motion capture as this incredible new place for us to go in performance that we never had before that’s more like kind of a puppeteering," Ruffalo said. "You no longer are constricted by the attributes that you have as a person your age or weight or size. None of that matters anymore."

10. Scarlet Witch is one bad b----h.

Of the new members to the team, Elizabeth Olsen's Scarlet Witch and her psychic abilities seem to have had the biggest impact among the crowd. "She’s able to bring out the worst in us," Ruffalo said. And if you need a more metaphorical explanation, "It’s like Sid and Nancy. She’s the Nancy. She’s everyone’s Nancy."

11. Banner has a special connection to The Vision.

Since "Age of Ultron" is shifting the origin of its villain to Stark creation, it was only partially surprising to hear Ruffalo refer to The Vision as "my baby." In the comics, Ultron created the hero, played by JARVIS voice actor Paul Bettany in the movie, but it sounds like Banner has a part to play.

Also: "He is so dope." -- Mark Ruffalo on The Vision

12. Hulk might talk more, but he also might not.

Since the decision about Hulk's word count can wait until post-production, Ruffalo and Joss Whedon were still deciding on that during my visit. "He’s not gonna have a soliloquy" was about as certain as Ruffalo could be.

13. Joss Whedon cracked the script right away.

As the self-declared "Mayor of Marvel," Downey's had a fair few experiences with the studio, including some creative "squeaky wheels." As Downey describes it, that didn't happen at all with Whedon's first attempt at the script. "I was done with the first draft, and I said, 'Cool. I like it.' [Marvel Studios president] Kevin [Feige] was like, 'Wait, what did you just say?'"

14. Downey didn't get to know Whedon until "Age of Ultron."

Not that it was Whedon's fault. "'Avengers' was so -- I don’t want to say disorienting -- but it was. It was this very kind of well-managed, compartmentalized attempt to do something unprecedented."

15. At this point, it's safe to assume Tony can't throw a party that ends well.

And that fact really amuses Downey. "I don’t know why that never gets old," he said. "Maybe it would get old if it happened again. But this time it still feels like it’s now the norm."

17. Expect a big finale.

Downey wouldn't elaborate, but hinted that a lot would happen in the final act. "I read the last page, and I got chills for a reason I definitely can’t explain," Downey said.

18. Paul Bettany was very uncomfortable making this movie.

As JARVIS, Bettany has been with Downey from the beginning, but he's performed the entirety of his Marvel Studios work from a voice-over booth. Now that he's on set, Downey is taking pleasure in watching Bettany play catch-up in a hot, form-fitting costume. "There is no one I would rather have the delight of seeing in the extreme discomfort than Paul Bettany," Downey said.

19. Quicksilver and Scarlet Witch's backstory has been tweaked and Joss-ified.

Downey remembered reacting to the origins of the newest Avengers and relishing Whedon's fresh approach. "That's the absolute coolest way you could have done it," he said.

We'll have more reports from the set, including interviews with Joss Whedon and Chris Evans, in the coming months.

"Avengers: Age of Ultron" opens in theaters on May 1.