My dog is almost 3 years old. Every so often, he seems like he's nibbling a very small object, but there's nothing in his mouth at the time. Sometimes his skin on top of his head jerks up and down rhythmically at the same time. He doesn't go completely absent, but he does still during these 'episodes'. I've tried to video it, but it only lasts 15-20 seconds at a time, so by the time I've got my phone out, turned on the camera and switched to video, it's finished.