Clankeyes-You know, now that you mention it one of my runners had a bit of a shiver also. I don't know why, but he does not do it any more. He is about 2-3 months old now. Maybe it is low niacin, just a bit weak. I haven't supplemented yet, but one of my younger ones that I just got seems to have a wobble, and after researching I think it is low niacin.