Apple Shake 4 Tutorials - Manual (Page 160)

160 Tutorial 4 Working With Expressions
Instead of a flat value before and after the two keyframes, the zAngle parameter keeps
the same slope into infinity.
8 Test the animation again with the Left Arrow and Right Arrow keys.
The animation continues and is matched beyond frame 5.
You are almost done. Honest.
To delete the Text node and apply the animation to the fan:
1 In the Node View, select the Move3D1 node and press E to extract the node.
The node is pulled from the tree, but not deleted.
2 Attach Move3D1 between the fan node and the Over1 node.
3 Delete Text1 and Mix1.
KeepValue mode KeepSlope mode