Trivia: Stan Lee makes his usual cameo, this time as a patient at the asylum where Selvig is being held.
Continuity mistake: In the scene where Thor tells Jane to hold on, she's on Thor's right side and Mjölnir (the hammer) is in his left hand. As they are traveling through the Bifröst to Asgard, the position of each has changed. (00:28:20)
Chosen answer: As seen in the film, the portals are in flux. They are constantly activating and deactivating, potentially pulling items through from one dimension to another.
MasterOfAll