What? As far as he's concerned, an arm around her shoulders is far more casual than if he'd held her around her waist. This is him being discreet.

He glances down at her, at her eyes, at her lips, the way her hair frames her face, and he glances away again to take another sip of his drink.

"You're welcome."

He gives her a light squeeze.

Thanks for coming with me. Thanks for being with me. Thanks for putting up with me.