Apple Motion 4 - Manual (Page 585)

The selected interpolation method is applied to all of the selected curves.
Convert to Bezier
Bezier interpolation method is the most flexible, allowing manual modification of the
curve. Motion lets you convert any keyframe into a Bezier keyframe quickly and easily.
To convert a keyframe into a Bezier keyframe
µ
While holding down the Command key, drag the keyframe in the keyframe graph.
Bezier handles appear and your mouse movement automatically controls one of the
handles.
Note: Command-clicking a Bezier point resets it to Linear interpolation.
To simultaneously modify the handles for more than one control point, Shift-click to select
multiple points, then adjust the tangents. If there are no tangents on the point, drag it
while holding down the Command key.
To break a handle
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While holding down the Option key, drag the handle.
585 Chapter 10 Keyframes and Curves