As soon as he received the news, Rex's mind paused for a second, stumbled at the words uttered by the person that he really hates right now. 'Wait, what...?' the possibility of that happening never crossed his mind, he hasn't taken it into consideration.
For a moment there he was shocked, Giana can tell from the sudden silence.
Endless possibilities entered Rex's mind as his mind was forced to consider the possibility that Kyran was not held hostage by humanity. Due to the bias that he has against Giana, he never considered that possibility, and even now he's still reluctant.
'Her heart beat and even her breathing are normal, I can hear it. It doesn't seem like she's lying'