Haha, I'm a moron. I can't believe I didn't realize what she was talking about
Most people call it 'snapping' their fingers.
I only snap my fingers when my rats are doing something I don't want them to be doing (fighting, bunching up towels, chewing on hammocks, et cetera).
My rats loooove being scritched behind the ear! They'll slowly close their eyes and brux in contentment