Why does the birdcage sing?

There hasn't been a lot of good finds at Goodwill lately: just a lot of holiday junk. But Mitchell found this wonderful birdcage, which matches the one I found in Austin. (Just so you know, the Terre Haute cage was 75% cheaper than the Austin one.) Apparently, the previous owners of the new one had it hanging, because there is a little bit of color discrepancy between the top and bottom, but it's still lovely and the matched set is going to look stunning.

We have a light in the first one, so they may both become some peculiar lamps in our new thrifted apartment.