You can pluck all of them to hear what they sound like (don't try this at home, kids, not without permission). But after you solve the triangle box in the captain's cabin on board the ship --
-- if you click on the langspil, the one hanging on the wall next to the flyer, you'll discover a neat little find-the-differences puzzle. Read to the end of this hint for a screenshot.
Hint 3
Look for subtle and obvious differences between the two halves of the design -- extra toes, missing ornamentation, circles that are doughnuts on one side, a bird looking the wrong way.
Hint 4
There are 11 differences to find; when you click on one, a little button at the left goes dark. That helps you keep track of how many you have left to find.
Hint 5
You can click on a difference on either side. When you click on a difference, that part of the design will go dark on both sides.
Inside, you'll find an odd thing called "Carved Star" in inventory. You'll need it for a puzzle on the ship that you probably won't find for a long time.