I've never given this much thought, but apparently the final roboticized voice in the Electric Light Orchestra's classic "Mr. Blue Sky" has a special message for listeners. And it seems to be one that people have been getting wrong for years. But Jeff Lynne has confirmed it's there, and he explains why they put it in so many decades ago. 

You can hear it for yourself in the video below, around the 4:50 mark. 

In case you missed it: Misheard song lyric in Mr Blue Sky revealed