Instructions
Shut the window shade in the office to make it dark.
Go to the desk and get close to the lantern projector.
Blow into the DS's microphone to activate the lantern. The lantern should project pictures of animals on the wall. Take note of the order in which the pictures are projected.
Go to the wall in the office that has paintings of animals.
Tap the paintings in the order given by the lantern projector. A secret alcove opens that contains the basement key.