My snowshoe polydactyl's eyes seem to shake or tremor back and forth very very fast. This seems to be when she is only looking straight at something. Is this normal?

I brought a new boy cat home to 2 preexisting sister cats. These girl cats are not affectionate. They are more like play cats to my husband. They don't even like being held or petted. I brought home a trial boy cat from a foster home that had numerou...