One of the most perplexing scenes in the newest Man Of Steel trailer is when Superman is shown apparently drowning in a sea of skulls. There have been various theories circulating online as to what is happening in that scene, but we have the actual explanation. If you don't want to be spoiled about what is happening in the skull sequence, then stop reading now.
The explanation below about the skull sequence isn't a theory and didn't come from an anonymous source claiming to have seen the movie. The information comes from a Man Of Steel tie-in book called Man of Steel: Inside the Legendary World of Superman.
In the book, it explains that the skull scene is actually a dream sequence. About midway through the movie, Zod subjects Superman to nightmarish mental torment. Zod tortures Superman with a vision of the Man Of Steel sinking beneath a mire of human skulls. In addition to the skulls, Superman is shown wearing an all-black version of his Superman costume. This dream vision of Superman "signifies the potential for even the greatest champions to grow corrupt." It represents that one path that Superman could take is that he could become a tyrant.
The Man Of Steel is scheduled to be released in movie theaters in the United States on June 14, 2013.