Steve Rogers: Stark, are you seeing this?
Tony Stark: Seeing, yes, still working on believing.
[Tony place his hand over his left eye and looks at some monitors.]
Tony Stark: How does Fury even see these?
Maria Hill: He turns.
Tony Stark: Sounds exhausting.
Steve Rogers: I think Loki is trying to wind us up. This is a man who means to start a war, and if we don't stay focused, he'll succeed.
Clint Barton: The Cube is a doorway to the other end of space, right? Doors open from both sides.
Maria Hill: When did you become an expert on thermonuclear astrophysics?
Tony Stark: Last night.
The Other: The Tesseract has awakened. It is on a neutral world. A human world. They would wield its power, but our ally knows its workings as they never will. He is ready to lead. And our force, our Chitauri will follow. The world will be his, the universe yours, and the humans, what can they do but burn?
Answer: During the end sequence of The Incredible Hulk Banner discovers that he can aim the Hulk in the right direction, give it a goal, which he uses to defeat the Abomination in that film. Key to that appears to be willingly accepting the transformation into the Hulk, which he does by choosing to jump from the helicopter. On the Helicarrier, Banner doesn't want to transform, it's caught him by surprise, he's fighting it, which is why it takes ages, is seemingly very painful and, as an involuntary change, the Hulk is out of control. In the final battle, Banner chooses to make the transformation, to "suit up", as it were, and thus the change is swift, painless and results in the cooperative Hulk capable of working with the others towards a goal.
Tailkinker ★