Nothing much actually made Fred go speechless. There were a good lot of things that could keep his mouth busy for a few seconds though, and a good snog was one of the best of those sorts of things.
He was surprised and unresponsive for about half a second, but then... well, hell. A pretty girl snogs you, and you snog her back, don't you? Even if she happens to be an employee AND the subject of the 'off limits' conversation you just had with your brother a week ago. She could kiss, and he kissed back and hand a hand on the small of her back pulling her up against him until she pulled away, then cheekily disappeared with him blinking a little wide-eyed after her.
A moment later he shook his head and then apparated after her, appearing just outside the Hogs Head and looking to see where she'd ended up.