Go to Disc Two, and choose the first documentary "Mr. Thornton Goes To Hollywood." At this point either select Chapter 11, "Lightnin', You're The Boss" or "Play All" and go to exactly 52:09 into the documentary. Once at that point, wait until you reach the part with the late John Ritter starting to explain the visual transformation of Billy Bob becoming Karl and you will see in the bottom right hand corner of your screen a silhouette of Karl sitting down facing the left. Quickly press ENTER on your remote to activate this button (this is the only way to get to this). Once there, you will see what John Ritter was talking about, showing on the film's set Billy Bob changing into Karl right before a few takes lasting only about 21 seconds total. After it plays the DVD will automatically take you back to the exact point in the documentary where you left off.
All easter eggs were generously submitted by SirDonk