Insert disc two and select either Fight or Convert when prompted. If you are a convert then press up on your remote from the 'Bonus' item to highlight the floor beneath Riddick.

Chronicles of Riddick: Director's Cut, The
If you choose to fight, then press left from the 'Bonus' item to highlight the blade.

Chronicles of Riddick: Director's Cut, The
Pressing enter on either of these will take you to a short piece (47s) with Colm Feore on set and complaining about his armour... all in good humour of course.

Links:
Easter Egg by Stephen Cowgill