My five-month-old girl Piper used to sleep downstairs in her crate, until we recently decided she was big enough to sleep in the bed with us and our other yorkie. She loves being in the big bed and snuggling with her pack, and the older boy accepts her being there...but she barks like a maniac. Even with all the lights out, she remembers that the first time she was up there she saw shadows on the walls. She presumably thinks the shadows are monsters (doesn't recognize her own reflection in a mirror, either), so she stays anxious at night and prone to fits of barking (we call this a RUDE AWAKENING for the rest of us who were sound asleep)
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During the day, now, she's started squeezing through the baby gate to go upstairs and bark at the wall where she saw the shadows.
I'm not sure how to stop this behavior and soothe her fears/obsession.