On their way back from Hagrid's, Ron is suddenly attacked by a large, black dog and dragged into a hidden passage beneath the Whomping Willow, a magical tree.
On their way back from Hagrid's, the three hear the sounds of Buckbeak being executed. Just then, a large, black dog appears and attacks Ron, dragging him and Scabbers into a hidden passage beneath the Whomping Willow, a magical tree.