Hook Modifier

As the hook moves, it pulls points from the strokes with it.You can think of it as animated.

The name of the object to hook points to.
Radius
The size of the hooks influence.
Strength

Falloff Type
This can be used to adjust the kind of curve that the hook has on the stroke points.You can also define a custom curve to get a much higher level of control.
Uniform Falloff
This setting is useful when using hooks on scaled objects,especially in cases where non-uniform scale would stretch the result of the hook.

The Hook Modifier stores points indices from the original strokes to determine what to affect;this means that modifiers that generate geometry, like a Subdivision Surface Modifier,should always be applied after the Hook Modifier;otherwise the generated geometry will be left out of the hook's influence.