I've noticed in many videos of great players that the bow stick rocks from one side to the other as the bow goes up and down.

Stick toward the player at the frog, hair edged away from the player  (underneath plane of the hair, like a ski base)....Flat in the middle, stick directly over the hair... stick toward the scroll at the tip, hair edged toward the player.

It's done in such a subtle way that i'm not sure if it's a conscious twist of the player or a subconscious twist just from the innate movement of the wrist as it moves up and down.