The most impressive of Johann Sebastian Bach’s pieces, musicophiles may have told you, will knock you over with their ingeniousness, or at least their sheer complexity.
A crab canon is basically a musical palindrome: a line (or multiple lines) of music that can be played together, backwards, upside down, etc. in complementary harmony. It’s a little difficult to grasp at first—most of today’s popular music doesn’t risk getting that intellectual.
I’m not a huge fan of Classical and Baroque era music (it lacks romance), but Jos Leys’ visualization of Bach’s Crab Canon is pretty fascinating.