Betsy has a nice post on playing Mahler recently. I've always really liked listening to Mahler, though I don't think I've ever performed any. And indeed, the bassoon solo at the beginning of the third movement is one of the more familiar tunes in the repertoire. I have it on my iPod, so I played it a couple times. And I realized something that I'd missed before: it's a round. Same melody, different instruments, starting at different times to overlap and generate the harmonies. Not sure how I could have missed that, but it seems obvious to me now.