On Disc 2, enter Trailers section. Once there, arrow to the LEFT. An eagle in Marcus Aurelius' chest should now be highlighted. Press ENTER and a Chicken Run trailer resembling the Gladiator trailer will play.
On Disc 2, enter the Storyboards section, and go to the second page where the storyboard deleted scenes are. There, select the "Rhino storyboards"; when you are on the first storyboard page press arrow UP, and the rhino will be highlighted. Press ENTER and you will go to a hidden menu with three options:
1) View a CGI rhino test.
2) View the script for that scene.
3) Return to the Storyboards page.
All easter eggs were generously submitted by Satelk