no need for a box. You put a camera after the second lens, and, if "things happen" between the lenses, the camera will fail to record what happens while the cloak is on. Not because the light has moved around the events, but because it has been split in two parts, a fast-moving and a slow-moving, leaving a short gap in time in which neither the fast or slow parts can interact with the events.

probable application: Magicians can make their tricks completely undetectable using a cloak while they do them (assuming they can do them in sub-microsecond time).