In Kennemur v. State of California (1982) 133 Cal. App. 3d 907, the Court found the trial court properly denied the appellant's request to call previously undisclosed witnesses. ( Id. at p. 925.) The Court clarified the meaning of the term "impeachment" testimony as used in the predecessor statute to section 2034, subdivision (m). The Court contrasted between foundational facts, which may be contested by a previously undisclosed expert, and expert opinion, which may not be so contested. The Court explained: "A party may impeach an expert witness by contradiction, i.e., by showing the falsity of any matter upon which the expert based his opinion. This can be done either by cross-examination of the expert or by calling other witnesses to offer evidence showing the nonexistence or error in the data upon which the first expert based his opinion." ( Id. at pp. 922-923.) The Court acknowledged the challenge a trial court faces in distinguishing between a foundational fact and an opinion, and cautioned: "In many cases, the ultimate opinion of the expert is based on a series of underlying opinions. Thus, rather than broadly construing what a foundational 'fact' is, the term should be strictly construed by the trial court to prevent a party from offering a contrary opinion of his expert under the guise of impeachment." ( Id. at p. 924.) In Kennemur, with regard to the proposed testimony surrounding the underlying traffic accident, the Court noted, "the photographs depicting the tire tracks and Mrs. Starner's testimony were the foundational facts upon which O'Shea based his opinion that the tracks belonged to the V.W. If appellant had sought to prove by expert testimony that the photographs were false, i.e., that they did not accurately depict the accident scene or that Mrs. Starner's testimony was inherently improbable, this would have been proper impeachment of O'Shea's opinions. . . ." ( Id. at pp. 924-925.)