Think of the head and ball as a pair of gears. As the ball (Gear #1) strikes the head (Gear #2) on the toe, Gear #2 turns to the right. As Gear #2 turns right, Gear #1 turns left.

When describing the horizontal gear effect, one typically talks about the benefit of the curvature on heel and toe shots. But,

what about center shots? Don't assume the center of gravity is located in the center of the face. As the hosel does had some additional weight, many times the CoG is located slightly toward the heel. In other cases, the CoG is intentionally positioned toward the heel. It should be more aptly phrased that the horizontal gear effect occurs when impact is made on the heel-side or toe-side of the center of gravity. Since the majority of golfers fade or slice the ball, club designers may shift the center of gravity toward the heel of the club on purpose. If the golfer hits the ball in the center of the face, but now on the toe-side of the center of gravity, the bulge