He's been so busy this year with Dumbledore's private lessons. Ron's been busy with Lavender. Hermione's been busy on her own and she enjoys the feeling of the three of them together in this little carriage, just like when they were all children. As they play, she takes out her Advanced Charms book and begins to revise, but it's almost abstract in her mind. Her mind turns over other things as she reads the Charms work and she's not sure which she focusses on more.