How have courts treated evidence on the element of intent in a murder trial?

evidence on the element of intent where a key issue was whether the murder was premeditated and deliberate and committed with express malice].) While defendant's choice of words may have proved prejudicial at trial, it was not unduly so. (People v. Karis (1988) 46 Cal.3d 612, 638 ["Undue prejudice" refers not to evidence that proves guilt, but to evidence that prompts an emotional reaction against the defendant and tends to cause the trier of fact to decide the case on an improper basis: 'The prejudice which exclusion of evidence under Evidence Code section 352 is designed to avoid is not the prejudice or damage to a defense that naturally flows from relevant, highly probative evidence' "].)