Excellent example of 'Cutting on Movement"

To ensure that you have smooth, unnoticed cuts between shots, it is best, if possible to cut on movement, so that you carry the viewers eye from one shot to another.

To help this, don't have the thing that is moving go completely out of the shot and have the moving object in the next shot starting just in frame, so that the momentum is continuous from one to the other - it is eaier to show it than to explain it so watch the clip and you should see what I mean.