Soft moans
Not to big, not to small either, just perfect.
He raised his hand up, and touch her right breast, pinched the nipple then draws it slightly. He took noticed of the fact that she didn't make a sound, or even moan. He could remember that the last two times he had touched her, she would always moan when he touched her on her boobs.
He grinned at her then touched her left breast, he pinched the nipple, just like he expected she moaned, "Ouch." Bingo!.