The basics of the explanation were simple enough to follow for the assassin, and for a few moments he thought he was successful in getting Stark to move on from the topic of HYDRA. He quickly found he was wrong.

He paused and stared at Stark, searching his mind for a concrete reason, but despite a few seconds' worth of thinking he could come up with nothing. He'd been HYDRA's asset for decades, executed who knows how many missions without fail until the most recent one. The only reason he left was because of a feeling he hadn't understood that conflicted directly with his orders.

So all he could give the engineer was his word, which wasn't very good, especially not when he still viewed the man as a threat. He looked to Steve, a plea for help in his eyes. He couldn't give a reason, but he really didn't want to answer the question with you shouldn't.