It can, apparently, draw Luxin out of a drafter if it touches their blood directly. It needs to touch their blood.
In cosmere, this should probably be silver.
Sarel mutters to herself before walking towards Longinus' outstretched leg. Her hand shakes as she scrambles up the carapace.
"Coming" she says the Rhythm of Determination. She hums a song to herself, soothing away her fear. Graduly, her hand steadies.