For the scene in which Marlowe is drugged, Edward Dmytryk showed Dick Powell falling through a sea of faces. He borrowed a trick from Saboteure (1942) by having the camera pull back from the actor to make it seem like he was falling. He also had the camera accelerate as it pulled back, to intensify the horror.
Dick Powell does not dance in the corridor of the mansion, as is often stated; he does a quick hopscotch on the checkerboard tiled floor.
For Moose Malloy's first appearance, reflected in the window of Marlowe's office, Edward Dmytryk couldn't get Mike Mazurki to appear large enough because the window was too far from the camera. Instead, he had a plate of glass placed between the camera and Marlowe's desk, then reflected Mazurki's image in that. On screen, the plate glass is undetectable, making the large reflection seem to be farther from the camera.