In the first one, Percy looks so excited. You can just hear him saying, "c'mon, let's go kick some butt". Annabeth is looking at him because she's worried that he'll leave her like all the others did and she can't go through that again. In the second picture, Percy look s more serious because he knows it's not a game anymore and Annabeth doesn't need to look at him anymore. she know's he'll be there for her.