If I had to guess the hardest scenes for Gary Oldman to shoot in the Harry Potter movies as Sirus Black, I would have said his death or the showdown in the Shrieking Shack, not necessarily the scene where Harry Potter casts his patronus at the frozen lake to save the Prisoner of Azkaban. However, despite not having to do much in the scene, that one was the hardest for the Oscar winner to shoot, and his explanation as to why is both hilarious and understandable.
Gary Oldman joined the Harry Potter cast during Prisoner of Azkaban as fan-favorite Sirus Black, and during that movie, he almost dies at the hands of the dementors who are trying to catch him. Harry saves him by casting a patronus charm while they’re on a frozen lake, and Sirus is so injured he’s simply lying on the lake. While on the Happy, Sad, Confused podcast, Oldman explained that this seemingly simple scene to film for him was actually the hardest to shoot. He said:
