Wide open. He will learn one day. For now, he does what Astarion says. Fortunately, he has experience in using the magic the Outsider gave him, so the process isn't so foreign.

He reaches for the power in the necklace instead of within and seems to find a well of - something. It isn't his and it isn't the Outsider's, but it's certainly a kind of magic. He focuses on the way that ravens look, how they move and fly.

There's a rush of air and light and Corvo the raven fluffs his feathers on the deck, spreading his wings out as if showing off to his companion.