if you study the video you posted you will see that the guy is controlling the speed to preserve the tail.
and at around 6-7 seconds when he moves fast (if you pause) you will see a trail of balls.
so he is either fading to destroy or reducing the size of the balls then destroying at a certain size
but you cant get rid of the balls , maybe just fine tune the reduction and destroy size.
but yea you could draw lines between the last 2 balls every tick and destroy them in line with the balls.
if you move fast though you will get a long line.
unless maybe you could destroy balls that are a certain distance from the curser
or destroy balls that are not overlapping another ball
hmm tricky one....