Okay, so this is essentially the same concept as the last assignment.  In the last assignment there was one object lagging behind the movement in another object, here however, one part of an object is lagging behind the movement of another part of an object.  In this case its an piece of seaweed.  The center of movement starts at its base, then the effect travels along the length of an object.  This concept can be used in a multitude of other areas, like the wagging of a dogs tail, or the sway of a girls ponytail.

Rough

Here is the first step in the assignment.  I first animated the spine of the seaweed to get the movtion and timing down before I jumped into animating the forms.  From this simplified version though, you can see how this concept can be used in the wagging of a dogs tail. 

Final 

The movement is of course way too fast.  I would have to go in and do quite a bit of inbetweens to slow it down to the speed what actual seaweed would move like.