He doesn't miss the sign, the silent thank you, he's far too close to her for that. He knows some of the avoxes speak with their hands, albeit quietly and in the shadows, hoping no one will see. Cassian sees because there's very little he misses anymore.

Her hand is wiped free of blood by the time Jyn turns back, though it hasn't quite stopped, already clotting again. He unscrews the balm and dips his own fingertip in.

"It was a very clean cut, and we have all the right supplies." He doesn't know where the teasing reply came from, mostly because he hadn't thought about it like he does with most conversations. It just... happened. Like it was easy. No angles to adhere to. He rubs the balm onto her hand, the sticky substance sealing over the wound. Hopefully it doesn't sting, but at least it seemingly helps staunch the bleeding. He unravels the bandage. "I think you are going to be fine."