I'm going through the second exercise, and I'm having an impossible time moving the actors into position. With an actor selected, moving the mouse left or right moves the actor left and right. Moving the mouse up or down moves the actor forward and back. How do I move the actors up and down? I'm sure its something stupid that I'm over looking, but I can't see it. Is there an easy way to select an actor when there are multiple models in the choreography, and is there an easy way to work with moving things around?