When my Yorkie was 4 months old .... she was sitting in the kitchen staring at her reflection in the glass door of the oven. She had convinced herself that it was another Yorkie staring at her! She stared it down at first...then barked...and barked.......then walked away so annoyed because the Yorkie wouldn't leave! Then she came back and did the same routine bark.........walk away......come back surprised that the "other Yorkie" was still there. She did this for about 4 minutes!