Ginny was still reeling from Percy's admission, her head felt a little spinny. Not that she was displeased about anything, the more she thought about it the better fit Cass and Percy seemed. It was going to take some time to get used to, but she would. Get used to it. And she wouldn't gossip about it, no matter how much she wanted to. At least, not until after the official announcement.
She saw Neville and Draco talking, and wanted to give them a bit of privacy. Besides, she'd spotted Harry talking with Snape, and she wanted to give him his annual birthday tickle. She waited until Harry and Snape were finished speaking and then snuck up quietly.
Without any warning at all, and disregarding anyone watching, she attacked. Digging her fingers into his sides she tickled with no remorse, and fully expected the consequences.