Instructions
Enter the office upstairs from the locked secret basement door. Interact with the window to shut the shades.
Approach the lantern and blow into your DS microphone to kindle the fire. Shapes of animals will appear on the wall.
Take note of the order of the animals being projected onto the wall, then tap the paintings of the animals in the office in the same order to reveal a concealed safe. This safe holds the key to the basement.
Exit the office, go downstairs and interact with the keyhole on the basement wall to open it.