After Jon layed down the porn magazine, he walked to his window and saw Karyn across the street. Through her bedroom window, he could see her studying at her desk. Without realizing that the stone was in his pocket, Jon said "I wish I knew how it felt to be a large-breasted girl like Karyn." After he made his accidental wish, he didn't notice the flash or even the heat from the stone.
Apparently, his grandfather's letter was wrong when it said that the wishing stone would only work by touching it. It only needed to be near the person using it, instead of making actual tactile contact.
Jon walked back to her bed and picked up her male-porn magazine, not realizing that reality had changed.
She remembered earlier when Karyn was complaining about her new enhancements and how she told Karyn that having large breasts wasn't all that bad. Jon of all people should know that, since she herself had lived with large breasts ever since middle school.
