Alex had noticed it for a while, he could tell that Alice was deep in her thoughts as she kept staring at the stars without any reaction to his eventual teasing.
(Teasing here is referred to Alex gently squeezing Alice's waist or caressing it.)
That something could be what she had been thinking on her own or making her own conclusions, and Alex didn't want that, so he asked.
"What's got you so deep in your thoughts?"
Alice looked at Alex trying to feign confusion.
"You know that acting of yours won't work on me, don't you?" Alex deadpanned her.
Alice turned her head lower in embarrassment.
"Out with it," Alex spoke as he squeezed Alice's waist, and finally he got some reaction as Alice straightened her back and leaned closer to him.
"It's nothing serious…." Alice muttered with her head on his chest.
"I still want to know, so tell me," Alex insisted.
