Food and water are delivered to the cells what seems like a good four or so hours later. But Hermione has no real way to tell time, so it's just a guess. She hides in a dark corner of the cell when she hears footsteps, thinking about how easily Malfoy had hurt her – how easily a real, loyal Death Eater or Snatcher might hurt her. She has to stay unnoticed, she thinks. Hidden. Safe. Invisible.