A bunch of new images from the Cleveland shoot of Joss Whedon's Avengers movie have hit the net and if online speculation is right they could reveal the threat faced by the superteam.
Forum chatter seems to point to the Skrulls as the most likely enemy, especially because of the alien-looking weapon seen in these images (top spot: the guy holding the weapon is wearing a Green Lantern T-shirt! ).
Motion-capture suits back up that theory.
A wikipedia history lesson for those less schooled in the Marvel Universe: "Skrulls are green-skinned reptilian humanoids with large pointed ears, red or green eyes, and corrugated chins. The Skrulls are known for their physical malleability and ability to shapeshift to any size, shape, or color at will, taking on the appearance but not the characteristics of other beings and objects."
The images were posted by fans on the Superhero Hype forums.