When Loki took control of Clint, there were some untold conditions. One of them was, that if the agent was to be taken out of Loki’s mental grasp unwillingly, he would lose his most useful sense. When Natasha fought the archer on the helicarrier, Clint tried to tell her, but it was too late. When she hit him hard on the head, his eyes went out like a light: Loki’s scepter sucked the light out of him as it left his heart.
I had shot a scene, speaking to a then uncast Clint Barton in a crane, and to see those scenes come together, and suddenly I had a scene with this actor, whose work I like so much, was a real thrill. — Clark Gregg