A couple of variations on this tacky theme.

My parents had a player piano that had a long piece of wood that could be
lowered betseen the strings and the hammers.  Attached to the piece of wood
were little strips of felt with metal "tacks" attached to them.  It gave a
somewhat honky-tonk feeling to anything played.

The 1868 square grand that I used to have had a similar strip of wood.  It
was curved and had very thin strips of a felt-like material like 'fingers'
too.  This strip was activated by the una corda pedal and slid the fingers
between the strings and the hammers.

Joel Hill
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Tallahassee, FL