Have the Game Boy Advance game Gyakuten Saiban in the cartridge slot.
Fast forward conversations
You can fast forward through long conversations by holding down the forward arrow on the bottom screen with the stylus. A fast forward symbol will appear and the conversation will be completed a lot faster than normal.
Hidden art
During the Case 5 ending credits on the touch screen, fingerprint powder will blown away. Eventually, a dialogue scene with a character will appear. Tap the touch screen at this time as though applying fingerprint powder to it and blow it off (as done during game play) A hidden drawing of that character will appear on the top screen.