His stomach rolls over because she is literally giving him explicit permission to get in her pants, which he has done before! It's been a few years, but everything else since reuniting with her hasn't felt like they've changed too much. It should even be better now, because they're older. They are consenting adults.

She sounds so calm, but he knows her still, and he knows she's panicking a little internally. Relatable, because it's Jyn and he wants this, he's missed her so much, but there's a baby in the next room. His nerves are on fire for too many reasons. What if he messes this up?

Cassian cradles her face and leans in, kissing her forehead. He lingers there for a moment, before moving to press his forehead to hers instead. Before the seduction must come reassurance! It's not going to be any fun if they're just freaking out the whole time, they can do this, it'll be fine. "Will you tell me if it works, or do you think I will be able to tell?"