Crab canon
canon.png|thumb|300px|An example of a crab canon. ]
A crab canon is an arrangement of two musical lines that are complementary and backward. If the two lines were placed next to each other, the lines would form something conceptually similar to a palindrome. The name 'crab' refers to the fact that crabs are known to walk backward. It originally referred to a kind of canon in which one line is played backward. An example is found in J. S. Bach's The Musical Offering, which also contains a table canon, which combines retrogression with inversion by having one player turn the music upside down.