What is the test for a judge to instruct a jury on the correct rule of law?

"[T]he judge must always be alert to the possibility that counsel in the course of argument may have befuddled the jury as to the law. If this occurs, then either at the time the confusion arises or as part of the final instructive process the judge should rearticulate the correct rule of law. Just as the law imposes a sua sponte obligation to instruct on certain principles of law in the first place (those rules openly and closely connected with the case) so does it impose on the judge a duty to reinstruct on the point if it becomes apparent to him that the jury may be confused on the law." (People v. Valenzuela (1977) 76 Cal.App.3d 218, 221, italics omitted.)