The fork
If the neighborhood moves when you think, it is not a shutter.
A gated curve cannot chase a strike map that migrates every third ball. That is a lesson. We say so before the paint is wet.
Orien will still ink the face. If the marks walk while you 'try to find the middle,' the shutter stays locked. We write a teacher name and keep your pass open for later, when the map sits still.
If the map sits still and the miss still wants gear, that is curve. That is why the row exists. We do not charge a lesson rate for saying the word lock.