imagine how scared rocky was. not just from his crew members dying, but because of how defeaningly silent it was. being so used to the constant drill of sound on erid to being alone in this silent unknown vacumm with no harmonies to help him see.
so when grace comes along, rocky really listens. he picks up on how grace's footsteps sound like if he's happy or sad; grace humming while writing calculations; hell, he even listens to the miniscule squelch of grace's eye blinking.
rocky went from being blinded, depending on the tendrils of his ship to let him see, to suddenly seeing so much of grace.
so i imagine, when rocky is watching grace sleep, he listens so intently to his mellow breaths and he looks. he can see graces' smiles lines, the stubble on his chin that he always scratches, the lashes that lay on his cheekbones. rocky wonders if all humans have so many things on things on their face (a face being a new concept to him too)
rocky has gotten so used to this new type of sound. it isn't as loud as his life on erid but it isn't silent as being alone.it's just right.
rocky found his sound in grace.