I started by c/t for any touching of the bowl with her mouth. She then started picking one up and throwing it down. Eventually I c/t for her throwing the one bowl down so it hits the other one. She was able to stack them easily when she is laying down and they are between her paws, but I didn't think she was really understanding what I wanted. She wasn't putting one inside the other consciously, just throwing it and it happened to go in. She didn't really understand the criteria I was looking for because when I had her stand to do it she would just throw one bowl down slamming it into the other one. So now I am having her put a smaller bowl into a larger one, c/t for each time she does it. As she gets an understanding of what I want I will replace the larger bowl with one the same size as the small one for stacking. It is hard not to help them with this trick by trying to put the bowl under the one that they are going to drop but try not to do this. Let them figure it out, just remember to c/t for the smallest movement towards what you want. Hope that helps.
Sarah
