Go into the "Special Features" section and highlight the Dreamworks logo by pressing left and then down. Press enter to see a credits sequence.
Go to the "Special Features" section form the main menu and you will see a Dreamworks logo hinted in one of the grass leaves on the right hand side of the screen. Select it by pressing the left arrow and then the down arrow key on your remote control, and you will be treated to a credit sequence with more 'antzy' music.
NOTE: This feature does not work on the DTS version off the release that does not contain any extra features.
This easter egg was generously submitted/corrected by DougieB