Hi,
I'm not a professional pilot, but perhaps I'll dare to answer your question anyway. I stand corrected should any of the more knowledgeable guys chime in and explain this in more detail.
The engine in question incorporates the cold stream (or blocker) reverser system. It's a reverse thrust system used only in high bypass-ratio turbofan engines - due to obvious reasons.
When a reverse thrust lever in the cockpit is actuated, air motor driven flexible shafts open the "blocker doors" (which you can see opening in that video) thus revealing cascade vanes. Cascade vanes divert the by-pass air out of the engine, propelling the air in a sightly forwards direction. This change of direction of the air mass helps to slow the plane down.
I couldn't quite find a good illustration of this effect by googling, but maybe
this pic will help you understanding.