Apple Motion 2 Tutorials - Manual (Page 18)

18 Tutorial 1 The Motion Interface
2 Once the add pointer appears, release the mouse button to drop the boxes layer.
3 Play the project (press the Space bar).
All of the objects in the boxes layer appear below the dolphin clips.
4 Drag the boxes layer back to its original position.
Note: You can also choose Edit > Undo Reorder (or press Command+Z) to move the
boxes layer back to its original position.