Josh Dallas was supposed to return as Fandral but commitment with his TV show Once Upon a Time (2011) prevented him from returning. He was replaced with Zachary Levi, who was the original choice for the role.
Because of the height difference between the two actors a box, and later a ramp, had to be used in the kissing scenes between Natalie Portman and Chris Hemsworth so they could reach each other's mouths.
The filmmakers chose Iceland as the setting for the dark world of Svartalfheim, for its black volcanic landscapes. The name itself, "Svartalfheim", literally means "Black elf world" in Old Norse/Icelandic.
There were about 30 hammers made for Thor of various weights for different uses. The main hammer was made from aluminum but it is replicated in different materials and weights, including a 'soft' version for stunts. Of the 30, five versions were used most often, including the 'lit hammer,' that emits light when lightning strikes.
Tom Hiddleston describes Loki as a "firework" in this film: "Well, where next? What's he going to do? What level of remorse does he have? If he does have any remorse or regret, why? Who does he feel guilty in front of, and who does he laugh in the face of? What's his motivation? If he stands to win, what does he stand to win? As a character you've got all these new motivations, but as an actor I am absolved from playing hero or villain - I'm just the live wire. And that was more fun than I can possibly tell you."
Filming at the famous Stonehenge historical site proved to be a challenge. After finally getting permission from English Heritage, the filmmakers found out that there were lots of rules and regulations associated with filming there. They could only be in amongst the stones outside of the normal visiting hours. So shooting had to take place early in the morning before opening, which only gave the film crew about three hours before they had to pull back for wider shots once the stones were opened to the public. Being a heritage site, no one was allowed to touch the stones or walk on any stones, so a lot of logistics had to be applied to the filming there.
At the end of September, Jaimie Alexander was injured on the London film set: "It was raining, it was dark outside, it was like 5 in the morning - and I went down a metal staircase and slipped and slipped a disc in my thoracic spine and chipped 11 of my vertebrae. I knocked my left shoulder out of place and tore my rhomboid on my right side... It took me out of filming for a month!"
In late 2011, Patty Jenkins was officially announced as director for this film. In December 2011, she backed out of the project due to "creative differences". Natalie Portman was reportedly so upset that talks between Marvel and Patty Jenkins broke down that she refused to return for the sequel but she was forced to return due to her contract.
The Asgardian waterfalls were based on the Dettifoss waterfall in Iceland, Europe's most powerful waterfall. An aerial camera crew flew to Iceland to film the Dettifoss waterfall from every angle to used as a base for developing the visual.
The stunt men and extras playing the Dark Elves had to go through a training period where they practiced standing tall and proud since the dark elves are envisioned to be a noble people. Prosthetics designer David White helped out too by designing the helmet so that the eye line was slightly pulled down, forcing the actors to tilt their heads slightly up and back, which gave them a very proud, strong feel.
According to Jake Morrison, the Asgardian skiffs in the film work in a unique manner: "The idea is that the Asgardians came to the Viking people with ships like this, and their technologies that inspired the Vikings to begin building their longships. When you see one of these skiffs move through the water and then suddenly take flight it just keeps that whole curvy, Stan Lee-Walter Simonson world of Asgard alive."
Adewale Akinnuoye-Agbaje described Kurse as "an amalgamation of a bull and a lava-like creature." For his role as Kurse, he underwent a daily three hours of make-up and 40-pound prosthetics: "I'm sure there will be a certain amount of CGI, but a good 80% was me in that suit."
According to VFX supervisor Jake Morrison, the Harrows, the spaceships used by the Dark Elves, are powered by black holes: "A black hole pulls in all directions. You stick a box around it - but if you poke a hole in one side of the box it would pull in that direction. So effectively if you strap a craft around that you've got a propulsion drive which is kind of an impulsion drive."
Jake Morrison redefined Thor's flight ability in the film: "He's jumping to attack somebody, it should be more of a lift and land rather than necessarily a straight-line drive. The thinking behind that is that he can control the weather so the wind can keep him aloft to allow him to have that kind of profile."
Alan Taylor wanted Asgard in this film to have a more natural look: "The first Thor was quite shiny and it was a very conscious, smart choice. I wanted to get more of a sense of the Viking quality, the texture and weight of history. They've been around for thousands of years." To achieve this, the crew filmed on the coast of Norway (particularly the Lofoten islands) for three days, capturing six hours of footage; Asgardian structures were then embedded over this footage.
Christopher Eccleston describes Malekith as a tragic villain: "What I thought about a great deal was revenge. One quote is: 'When you seek revenge, be sure to dig two graves.' I did a film called Revengers Tragedy (2002) where I played a guy called Vindici-from the word 'vindictive'-and he is the distillation of revenge. So, in a way, that was what I had to think of: how revenge can make you absolutely monomaniacal-though you're still trying to make it recognizably motive-led. It's just the personification of movie evil."
This was cinematographer Kramer Morgenthau's first digital film. Morgenthau used an Arri Alexa Plus camera, with Panavision anamorphic lenses: "The lenses brought some of the magic and mystery of photorealism back to digital, that big-movie look."
Joss Whedon was brought in to do uncredited rewrites for a few scenes, including the extremely brief encounter with the stone creature (which was originally a much longer scene) and Loki briefly masquerading as Captain America in a hallway conversation with Thor.
When Eric Selvig is in the mental ward explaining the convergence theory, on the blackboard behind him is the familiar Yggdrasil tree drawing of the 9 realms. If you look closely, one item circled says "616 Universe" 616 is the assigned number to the Marvel Mainstream Universe.
In the film the substance the Dark Elves are after is called Aether. Aether is the mythological personification of the sky in Greek mythology and later in alchemy and medieval science the material that fills the region of the universe above the terrestrial sphere. A reason of the use of the word "aether" can be because of its connection to dark energy which the Dark Elves are connected to in this film.
Jake Morrison described the final battle as Time Toffee: "As you punch through from one realm to another it's almost like a slightly gelatinous membrane you have to pass through. It bends a little bit then rips and spits the person out."
According to Natalie Portman in an article that appears in the New York Daily News. During the post credit scene where Thor and Jane Foster finally kiss. The woman in the scene is not actress Natalie Portman as she was unavailable to film the scene, but Chris Hemsworth's actual wife Elsa Pataky