Something. There had to be something Arialla could do, some blessing she'd received, that gave her a leg up on the others climbing the tree. (She would have believed it more if Wessex had not been one of the others.) But she wasn't about to try to harm someone over this prize, to try to get in someone's way -- even if she'd been that kind of person, Mabel's fate had shown how easily that could backfire. So instead she threw all of her effort into climbing, her feet and hands still shifted into eagle's talons, her bones and body partially shifted to be lighter, like the eagle's. She could only hope for a straightforward race to the top -- she could only hope to be faster than everyone else.
Arialla uses her partial eagle shift to be lighter than usual, and to make her feet and hands into talons so she can grip more easily. And she climbs!
please don't take my sunshine away
