we had a silimier thing happen once, my dogs are never left alone to play without anyone around, when nobody is there 4 are kenneld and Happy is loose. when Happy was a puppy, she and perky would be put in the bathroom together when we were gone, and they would play, one day Happy got her jaw stuck in perkys collar, after that collars always came off when they were together without supervision, and now the dogs are never together without supervision, with 3 its just to keep em out of trouble, Perky is only locked up to seperate her from Happy, cuz Perky hates Happy.