I've been flying a lot lately and one of the things I've taken notice of is the insane sound of the engines doing reverse thrust upon landing. Reverse thrust, in a very simple explanation, is when the engine opens up in such a way where the air being pushed through it is reverse in order to help slow an aircraft down. The split in the engines you see in the video above is this action taking place.
Here's one more marvelous one shown on an Airbus A380.