That scowl may be unnoticed by Firo, but Rey certainly takes note of it and wonders if it's something she's said, rather than a thought he's having about some asshole FBI guy. What does she have to say to convince him that she's not trying to remark against his competency?

And that's when a stupid thought occurs to her.

"Because of this."

Rather than explaining it, she lifts her hand up. Enough distance is put between them and the surroundings that it should be safe. Then her hand goes up in flames.

It's a small fire, crackling from her fingertips to the palm of her hand. Hopefully it should get the message across as to why she feels prepared enough to enter the caves, despite not being armed to the teeth.