Jewel was padding around checking on DH and me, with us being in separate rooms. Suddenly she starts alarm-barking in the bedroom near where DH was.
I eventually go to see what's happening.
She's in the doorway, still barking, hackles up..... room looks normal. Nothing out of place.
She's looking at the closed closet door, on which hangs Thing2's gi, his Scout uniform, and his Halloween costume.
Which has a blank-face Michael Myers style mask on it.
I took the mask down.... and yep, that was it. She didn't want it near her. I put it out of sight on top of the book case and everything was ok again.
