For Harry Potter and the Chamber of Secrets, the temperamental tree began as a sketch from the Art Department, which had to be turned into a real Whomping Willow. Mr. Weasley’s flying car WAS ‘whomped’ by mechanically driven branches, according to Special Effects Supervisor John Richardson and his team. For the Whomping Willow’s appearance in Harry Potter and the Prisoner of Azkaban, a full-size tree trunk was created on set, with branches added digitally in post-production.