That seems a little arbitrary to me. You have to switch how you hold the brush to go left/right (unless your brush is double-sided). For example, I can't imagin

That seems a little arbitrary to me. You have to switch how you hold the brush to go left/right (unless your brush is double-sided). For example, I can't imagine his first move, from upper left outside, to upper right outside, to be continuous. And you might as well argue that you're not interrupting either when going from top to bottom. I mean you're just continuing the same movement after all. Damn, who knew brushing teeth could be so complex.