The Juno Minute.

This is the 60 seconds* of a tune chosen by on-line record shops for the 'Listen' MP3, which bears no relation to the rest of the track.
You'll think you've bought the finest Ambient available to humanity, but will in fact receive bastard-hard nose-bleed Techno. The Juno Minute will have been the breakdown.
You'll have gone looking for some tracky Deep House, but the postman will hand you full-on-gospel Garage. The Juno Minute will have been the first minute of the track.
* - Pedants pointing out that Juno's clips actually last 90 seconds will be wedgied. They used to be a minute long.