Skitter is the bodily bouncing of a plane provoked by the shock of the cutter hitting the leading edge of the wood. This makes the plane bounce, land again, cut a bit, bounce again and so on, rather like a stone skittering on the surface of a pond.
This results in deepish marks, unlike chatter marks since these are fairly well-spaced. Loose frogs and loose lever caps can increase the possibility and severity of skitter, but even with a tightly-tuned plane it happens to all of us.
Chatter is evidence of a plane's misbehaviour that produces regularly spaced very shallow marks very roughly 1mm apart or less. Look for a slack lever cam failing to properly hold down the cutting iron.
In fact,the only way I could get my Stanley smoother to do this was to so loosen the lever cap screw that the lever cap almost rattled as I worked.
The lever cap setting screw should be so adjusted that one can only just release the lever with finger and thumb and the feed wheel can be conveniently operated. Naturally, the cap iron should be a good fit against the cutting iron.
Have a sharp iron.
Slightly slew the plane, say up to 20 degrees, so that the cutter meets the wood at an angle.
Adopt a very deliberate military style "Plonk plane down. Pause two-three...... Push. Pause two-three"......., and so on.