My cello teacher showed me a new tune yesterday, Mozart’s “Canon Inversus”. It is an interesting little piece – some site I just googled mentioned something about Mozart discovering Bach in connection with it, so I guess it’s something clever Bach would also have done. It is a piece for two cellos (or two violins or two violas, depending on how it’s arranged). But instead of the two parts being written on parallel lines one above the other and played from two separate sheets, this is all on one piece of paper. The musicians sit down facing each other, the paper in the middle, and one plays from top to bottom, the other plays it backwards, from bottom to top.
It sounds k3wL too and has a neat Apocalyptica-type sounding bit in the middle.