Moon
Most of the time, he prides himself on his ability to read her moods. He has always been good at interpreting facial expressions- which was an ironic ability to have, back when he was in the armour, when not even the most perceptive of people could have picked up on the way he was feeling merely by looking at him. In recent years, he has become something of an expert at reading body language, too; and by now he is able to vaguely sense her emotions purely through the sound of her breathing and the way she moves.
Tonight, however, the moon is obscured by a thick curtain of clouds, and the sounds of the stream and the night seem louder than usual, and he is distracted by the sensation of the wind, and the grass beneath his bare feet, so he has no idea what she is thinking.
Perhaps she has become used to him being able to predict what she wants before she even asks for it, because when the tug at his sleeve eventually comes, it is sharp and impatient, and demanding.
In the darkness, he turns his head, and all his senses instantly focus on her form. The second he sees her face, made expressionless by the lack of moonlight; and hears her almost soundless breathing; and feels the way she is shifting her weight almost imperceptibly beside him, he knows exactly what it is she wants.
It doesn't take the light of the moon to show him when Winry wants a kiss.