In Cantu v. Peacher, 53 S.W.3d 5 (Tex. App.--San Antonio 2001, pet. denied), the Court concluded that when determining whether an affidavit is a sham, the court must examine the nature and extent of the differences in the facts asserted in the deposition and the affidavit. Id. at 10. "If the differences fall into the category of variations on a theme, consistent in the major allegations but with some variances of detail, this is grounds for impeachment, and not a vitiation of the later filed document. If, on the other hand, the subsequent affidavit clearly contradicts the witness's earlier testimony involving the suit's material points, without explanation, the affidavit must be disregarded and will not defeat the motion for summary judgment." Id. at 10-11.