Hunchback 40 is a unique burr, which is named after the peculiar burr pieces that construct it. Most of these burr pieces have extra protrusions that give them a "hunchback" appearance.
Many of Alfons' 18 piece burrs have burr sticks with a 2x2x8 dimension but these "hunchback" pieces have 2x3x8 or 3x2x8 dimensions. These strange burr sticks result in a burr which requires more studying of the pieces than just random pulling and prodding.
The "hunchback" pieces restrict movement to many adjacent pieces.