Castiel isn't shy about his body. With all the things that he's been taught, that might be surprising - he bares himself to Sam efficiently and without much hesitation, unashamed of his body. He's made sure to stay desirable and beautiful, and Sam will reap the rewards of what Castiel has sown. The omega knows what he looks like, and he knows it's good.

What has his eyes widening is every inch of tan skin revealed on Sam's own body. It dries out his lips, makes his breath stutter a little, because he hasn't really been prepared for Sam himself to look so appealing to his own eyes.