Chris Hemsworth stands 6'3" tall, and he put on 20 pounds of muscle to play Marvel Comics' hero, Thor. He is equally adept at swinging his fists as he is a mythical hammer. So who in the world would actually volunteer to be punched by him? Tom Hiddleston, his costar in " Marvel's The Avengers ," is who. Hiddleston reprises the role of Loki -- first seen in last year's " Thor " -- the adopted brother of the god of thunder with an apocalyptic case of sibling rivalry. Loki assembles an army to conquer the planet, and it will take the combined strength of Earth's mightiest heroes to stop him. Naturally, the climactic battle for the planet culminates in Thor and Loki coming to blows, and when I sat down to talk to Hiddleston, he explained that the hits you see on screen were real. Hiddleston said that when they were shooting the fight scene, "Joss [Whedon, the director] came over and said, 'Guys, I'm just not really ...