How does J.K. Rowling use imagery in Harry Potter and the Deathly Hallows?

Imagery:

"Dominating the scene was Hagrid, wearing a helmet and goggles and sitting astride an enormous motorbike with a black sidecar attached. All around him other people were dismounting from their brooms and, in two cases, skeletal, black winged horses."

"The book had broken free from its restraining belt and snapped viciously at Ron's ankle."

"Mad-Eye Moody's voice whispered out of the darkness, making all three of them jump back in fright. 'We're not Snape!' croaked Harry, before something whooshed over him like cold air and his tongue curled backward on itself, making it impossible to speak."