Rocker Nick Cave has `stolen' his twins' Christmas organ so he can make joyful music. The dark Aussie singer-songwriter admits his seven-year-old kids' toy piano, complete with a "boom-kchh, boom-kchh" beat track is ideal for helping him compose tracks. He tells Britain's Mojo magazine, "I took it off them and wrote four or five songs on that. You can't write anything that isn't joyous on this f**king thing."