My guess is it's been a few years since Farmer Derek Klingenberg played his trombone on a regular basis, but the cows don't seem to mind a bit. I'm not slamming Derek's efforts. I just know that if I picked up my trumpet after quite a few years it would sound somewhat similar to this. Hahaha. So, I'm basing it on that. 

Whether or not the performance is flawless, really, is completely irrelevant. It's all about the effort and......the cows. If you don't want to wait, fast forward to about a minute in. The minute it takes for the cows to come into the picture, however, squashes any possibility of this being rigged in some way. This is simply fantastic.