I don't know if this is normal, or what. My 4 month old silkie has been doing this for as long as I can remember: she jerks and shakes her head. Kind of like when a dog shakes its head because something's bothering its ears or something. And she does it almost constantly, at least a few times a minute. It doesn't seem to bother her and none of the others do it. Is this normal, or is she just weird?