Bella produces a ball of thread, hands an end to Tony - who's less likely to suddenly need her hands free - and unravels it into the cave. (This is a standard cave precaution if you don't know where you're going.) It's a smallish cluster of caves, not just a single cavern nor yet a node of a large network like the Caves of Chance or the Caves of Fire and Night, and she pokes her head into each of them, not explaining herself to the wizards or their female and therefore nonwizard family members. None of them tries to attack her. She rolls up the thread and comes out again.

"There are some wisps coming in, but it's unused residue, not uprooted useful magic. The same sort of stuff my marble grabs," Bella reports when she's retrieved the end of her thread from Tony.