This is an excerpt of Austrian composer Alban Berg's most avant garde and experimental pieces for clarinet and piano, which I performed graduate student Stephen Dubetz last semester! The score calls for the pianist to silent play a cluster of notes in the right hand while violently attacking the lower register with the left hand. The effect reverberates the treble strings creating the "ghost" of a chord. You can barely hear it at 19 seconds in. Wild stuff for being written over 100 years ago.