S-4 does notice that crinkling, and he provides the sigh of relief. Apparently whatever magic he could offer was enough, and didn't provide them any pain. They still look like a normal human. It should be fine...

He still checks their arm over for any other injuries, but after a few moments, he reluctantly lets go and offers a nervous little smile.

"You're welcome," he says softly. Not that he should really be thanked. "A-And it's okay. As long as Serif didn't wake up, I don't mind. I'm just... glad you trusted me."