The Cube

An expert woodworker took two pieces of solid wood, and carved them in such a way that they could be put together as in the image shown below. The cube, you may assume, looks the same when viewed from the other side. The two halves are solid and contain no separable or moving pieces. The halves are, as they appear to be, interlocked. You could easily pick up the entir cube by just grabbing the top half.

How did the woodworker create this cube? Your solution should not contain the word "glue" (originated from Grey Labyrinth's website).