Continuity mistake: For a brief moment during the battle at the end, the scar on Tony Stark's left cheek vanishes after saying "I will, roger that" to Hawkeye. It reappears shortly afterwards. (01:54:15 - 01:54:55)
Continuity mistake: After Hulk smashes Loki against the floor, the amount of rubble around Loki changes between shots. (01:55:25)
Continuity mistake: During the big battle against the Chitauri, Captain America is zapped with a blaster bolt. When Thor helps him to his feet we can see a significant amount of damage done to his suit, just below the star on the right hand side. But later on after Iron Man destroys the Chitauri ship with the nuke, the damage is completely gone. (01:59:25 - 02:02:40)
Continuity mistake: When Tony goes after the nuke, there is a huge cut visible above his right eyebrow (or viewer's left). Later on after his face mask is removed, his right eyebrow is completely visible in the shot, even with the helmet in the way, and the cut is nowhere in sight. (02:00:00 - 02:03:00)
Continuity mistake: When Thor lands beside the overturned car on the Park Ave viaduct in front of Grand Central, the car has a dent between its fender and tire, but in the next closeup that dent has vanished. (02:04:10)
Continuity mistake: After the big battle, Iron Man lies on the street when Capt. America, all dirty and messy, says "We won." Iron Man sighs in relief and rests his head on the pavement. A frame later, from a wide angle, his head is raised, plus Capt. America's face is clean and his hair is brushed. (02:08:30)
Continuity mistake: When Maria Hill is being attended to after she gets hurt, her earpiece is on the left side of her face. In the next shot she is talking to Nick Fury and her earpiece is on the right.
Continuity mistake: When Rogers, Banner and Stark are discussing about Stark Tower, the tools on the table move around.
Continuity mistake: There is a deleted scene of Steve Rogers looking through the files of his former comrades. When he first reads the sheet for Peggy Carter it has her address printed in a modern typeface on a label stuck to the page. The next time we see it, the details are the original typeface on the original paper.
Continuity mistake: Towards the end while the Avengers are on the news, there is a guy spray painting "the Avengers" on a wall. The style of the letters changes between shots.
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 ★