The first he noticed of her was a mild jinx which sent a shiver running through his body.
"G-ginny?" The word fell out of his mouth in startled disbelief. She never sought him out. Now though, she looked completely comfortable in front of him, as though it was completely normal for her to be there.
"Do you know how long I've been trying to get your attention?" Not only had she jinxed him, she was now glaring at him, and Harry found himself tongue-tied.
After a moment, Ginny continued. "That library book is overdue," she said, waving a list in front of his face. When Harry squinted, he thought he could make out the heading 'Overdue books.' Harry took a deep breath and tried to focus on what she had said.
"Yeah, well, I kind of need it," he replied eventually.
Ginny rolled her eyes. "Well I need to take it back to the library. Someone else might need it, and your week's reservation is up." She stood there expectantly, her arm outstretched and a challenge in her eyes.
Unable to avoid it, Harry handed it to her reluctantly, muttering "Well don't blame me if the final task kills me. Why are you collecting books, anyway?"
"Detention," replied Ginny vaguely, as she walked off, presumably to collect more books from her list.
Is she telling the truth? You'll never know. Anyway, a nice bit of interaction for them in fourth year.