The bird is attentive, watchful, waiting, and this anticipation speaks of an exchange that has occurred before - the bird expects something, and after a moment it becomes clear what.
The button balances on Cherny's thumbnail for just a moment before he flicks, sending it spinning in a gleaming arc over the crow's head; the bird croaks excitedly and tracks its path, moving even before the missile lands among the leaf-litter some feet away, hopping after it in ungainly pursuit. The fledgling searches with apparent enthusiasm, flinging dried leaf litter about until - aha! - the button is found again and the bird immediately gallops back with the trophy gripped in its beak; it deposits the button in Cherny's outstretched palm before gaping its beak and fluttering its wings in plain anticipation of reward, croaking frantically to be sure it has the boy's attention.
Previously he'd only winked, or glanced sidelong, of perhaps half-smiled, faint and faded echoes of his more customary expressions, dulled by that desperately-maintained distance; in the moment, though, as the crow returns with a dull brass prize and the mill-boy looks to his sister, there is a flash of the Cherny of mere days ago, a pleased and toothy grin. He reaches for the seamstress' stale crust, then, to tear off a pinch of bread and offer it to the crow in payment; the morsel is siezed and gulped down with gusto, and a clack of the its beak and croaking call makes it clear that the crow is ready to repeat the trick, the game. By this point others among the foraging flock have taken note and start making their way over - none quite so bold as the first, but all quite interested in what's going on and particularly the nuggets of bread to be earned.
At which point Cherny presses the button into Gloria's hand and nods encouragingly.