It's a goof: the cubes are 2 different shapes in the film.
In the beginning when Joe first picks one up, it's a perfect cube with little bumps.
Later (when he's in the bath, and when it starts vibrating) it's not a cube any more.
If it was intentional (part of the story) I would think SOMEONE would have mentioned it...
22.214.171.124 20:45, November 12, 2012 (UTC)