Clint was trained to watch. It was what Clint did, he watched; targets, places, people in general. He noticed reactions, ticks, nervous habits, changes in pupil dilation. He was the one that picked up on the little details that were overlooked in the grand scale of things. It was why he perched, why he needed to have the birds eye view, despite the jokes it always came with.
He noticed when Barnes braced for the start of whatever HYDRA programming would normally be, noticed the mild surprised, if it could be called that, when whatever Loki was doing didn't bring that, and then the confusion.
"There was a flaw in the previous method, you probably noticed it yourself," and Clint was mostly banking on the fact that James' programming had been degrading the longer he'd been out of stasis, the longer he'd spent with Jefferson, "This will clear out the layers of programming, back to the basic... starting point. It's to stop what happened with Diana happening again."
There were times when Clint was just his usual self; he was restrained and controlled like Natasha, he'd never been that type of agent, his personality bled through far too often for him to ever be the perfect agent. But he had the capability to put on the persona from time to time, let the anxious constant energy he held just settle until he sat, still as stone with nothing but seriousness.
He could perch for hours with one target in sight, and while James wasn't a target, he was the only thing they were focusing on right then.