Hermione quite honestly felt like she was having an out-of-body experience at that point.  Draco had rested his head on her thigh and she could feel that he was panting.  She peeked down, trying to gauge how he was feeling, when she noticed his trousers were hanging open, one of his hands down them, probably willing his erection to behave.  A small giggle burst out of her at that thought and he whipped his gaze up to hers.