The Whistling Gall!

Well, I know it's a stretch, but that's how this little fella at the back looked to me.  Actually they are galls on a red-gum leaf.  Galls are very common on eucalypts. Here is a description from Sustainable Gardening Australia:
"Hi, my name is Gall (of Australian Native Trees).  Guess some people would describe me as an abnormal growth on plant parts, but I reckon I'm just a regular lump, hanging around on stems, leaves, buds and when the mood strikes...roots! I may look pretty boring (and a little ugly) on the outside, but I'm actually really interesting under the surface! Size wise, I can go from minute to big and hideous, and my colours can vary from red to yellow and even brown. I am the result of the plant cells' reaction to invasion by my friends e.g. wasps, beetles, moths, coccids, psyllid or bacteria. I don't move around at all (I just hang out growing bigger and bigger) and, once I've settled in, I stay for a long while."
I thought this summed it up well, but I didn't find this bunch hideous at all because I swear I can see a happy gall at the back whistling to anyone silly enough to believe that's what it's doing..... Are you still with me?