EMSL writes -

Here’s an neat idea for a jack-o’-lantern: Hide a single white LED just beneath the thin surface of the pumpkin. And program it with the same slow “breathing” effect that indicates sleep on Mac computers. The result? A pumpkin that sleeps like a Mac. It’s actually quite striking, in part because the effect becomes invisible every few seconds. It’s also an easy microcontroller project: our demonstration video and build instructions follow.