smooth is a musician. In some songs (often to provide variety in the song), the music will go up a whole or half step. Modulation down is less common. In either case, this is called a key-change - the key the music is being played in has changed.
Go to this page and click on the videos. They're set up to show off the key change. Once you hear them you'll know.
http://www.overthinkingit.com/2009/0...ic-think-tank/