In what circumstances will a court declare a mistrial?

Third, in People v. Smith (1970) 13 Cal.App.3d 897, the trial court declared a mistrial after only speaking with the jury foreperson and without polling the individual jurors. (Id. at p. 910.) However, the jury was in open court when the foreperson indicated that the jury was deadlocked. When asked if the jury wished to deliberate further, the foreperson replied in the negative. The court declared a mistrial and excused the jury. The appellate court concluded "there was adequate compliance with the requirement that the trial judge probe the rigidity of the deadlock before discharging the jury." (Id. at p. 911.)