Bob & Duck

Bob - similar to slipping except it also incorporates a ducking motion. So as your head is moving to the side and also downward. 

To execute the move, push off the floor with the foot opposite the direction you are moving, moving your head to the side, rotating the upper body and lowering down by bending at the knees. 

-Lead Side Bob - Bobbing to the side of the lead leg.
-Rear Side Bob - Bobbing to the side of the rear leg.

Note: From my studies, it seems most coaches don't teach the bob as a separate defensive motion and instead just think of it as a form of slipping. My first JKD/boxing instructor taught it as a separate technique, which is why I keep it as a distinct technique.  That said, it is similar enough to a slip that essentially everything discussed in the Slip section applies to the bob, so I won't recreate the wheel and instead ask you to refer to that section.

Duck - Moving under a punch by bending at the knees and squatting straight down. Drop down only enough to evade the oncoming punch 

Ducking with step and slide *Tutorial