Sam takes Bucky's hand, pressing his palm flat against the hollow of Sam's throat, fingers splayed just barely up his neck. The placing is purposeful, aside from wanting to show Bucky that there's no cut there - like this Sam trusts Bucky with his life, but he knows Bucky has more doubts. There's no strategic advantage to having a hand on Sam like that, no way to strangle him - it can only be about touch. Same reason he first tangled his fingers with Bucky's way back on Concordia, taking touch and making it something unfamiliar.

( I'm the only one who gets to make the call on whether or not you failed me. Pierce didn't ask you for anything, I did. And I'm so damn proud of you for trying, sunshine. )

Whatever guilt Sam feels about asking in the first place - it's not the time for it. Right now he's gotta focus on trying to tread water enough for the both of them until Bucky's got something he can hold onto.