The echo is the fun part. It's the forming and expanding of the welts, thus, the expanding of the degree of pain.

That's why in the traditional british canning, there is a time gap for the person holding the cane to pause intentionally in between each stroke. He does that so that the sub can receive the full treatment of the echo part, in fact, the pause should be around 30 sec. When the sub fully feel the effects of that stroke, he then moved on to the next stoke.