SHOWING A KNUCKLEBALL KNUCKLING.
SHOWING A BASEBALL KNUCKLING. Nick sent me this animated gif 
of R.A. Dickey’s knuckleball. (As I understand it, the gif (graphics interchange format) operates as a series of images.) Notice how this particular pitch starts out to Dickey’s right and then changes direction and moves to the left.
For non-baseball fans, the movement of a knuckleball is different each time. It is said to “dance”.