The key to getting these is the short animation of bigfoot running across the screen whenever you click on [Special Features] or [Chapter Selection] on the [Main Menu] screen:
Clip #1 - Can be found by clicking on [Special Features] and then when the bigfoot animation plays hit your [Chapter Forward] button. This clip will also play if you click on [Chapter Selection] and hit your [Chapter Back] button during the animation.
Clip #2 - Can be found by clicking on [Special Features] and then when the bigfoot animation plays hit your [Chapter Back] button.
Clip #3 - Can be found by clicking on [Chapter Selection] and then when the bigfoot animation plays hit your [Chapter Forward] button.
Clip #4 - The easiest way to get this last clip is to make your way to Clip #2 and then while that is playing hit your [Chapter Back] button again. Alternatively if you watch the [Deleted Scenes] and hit [Chapter Forward] right at the end, you will also be taken to this clip.