Beneath the superficial pattern lies a 3D shape not immediately visible to the eye. But with sufficient patience, should you continue to stare at the pattern, sooner - though often later, the obscured 3D form will emerge before your eyes and hover there, as if magically suspended in the surrounding chaos.

Stereograms are fascinating because they can remain utterly infuriating until the hidden object is revealed. But once seen, the image is so obvious that you're almost certain you wont lose sight of it. However, with the slightest adjustment of the eye, the image quickly disappears, at which point it is necessary to begin again; even if the task is considerably easier simply by knowing what you are seeking.

With continued practice it becomes possible to stare at various stereograms and pick out the hidden images fairly quickly. The trick is in adjusting your gaze so that you are almost looking through the pattern in front of you, at the same time trying not to look too hard. In that way the eye almost comes to rest on obscured object.

Now I suppose you want to know what the object is hidden beneath the Christmas lights and tinsel. Clue: A flying saucer hovering in space.

When two lines cross, the image does not show which line is in front and which is behind. This makes the structure ambiguous. It can be interpreted in three different ways. As two cubes i.e. when staring at the frame it will seem to flip back and forth between the front face (viewed from above) and rear face (viewed from below). Or as no cube at all, rather a two-dimensional drawing of twelve lines. So what are we seeing? Or perhaps we should ask, who is seeing what?