Today while tuning up my viola and mandolin, I noticed that I instinctively held the pedal on the piano which I was tuning to. To my surprise when I strummed a chord or a double stop, then muted my strings, I still heard the chord.

For a while I couldn't figure out what was happening, until I realized that it was the piano strings resonating at the same frequency as my instrument! *High five it's actually in tune *

Any similar experiences by you guys out there?