The judgment of the court was delivered by
DOHERTY J.A.: —
 The respondent, Mr. Suarez-Noa, stabbed and killed
Ms. Tanya Cowell. He was charged with second degree murder.
At trial, Mr. Suarez-Noa admitted to killing Ms. Cowell, but
claimed that he did not have the intent required for murder
or, alternatively, that he acted under provocation. The jury
returned a verdict of not guilty of second degree murder, but
guilty of manslaughter. The trial judge imposed an effective sen-
tence of 11 years.
 The Crown appeals from the acquittal, advancing two
— Did the trial judge err in law in leaving the defence of prov-
ocation with the jury?
— Did the trial judge err in law in admitting the expert evidence of Dr. Gojer or, alternatively, if the expert evidence
was admissible, did Dr. Gojer go beyond the proper limits of
that evidence in his testimony?
 For the reasons that follow, I would allow the appeal and
order a new trial on the charge of second degree murder. Significant parts of Dr. Gojer’s evidence were inadmissible. Those parts
of his evidence had a prominent role at the trial. The Crown
has satisfied me that Dr. Gojer’s evidence may very well have
affected the outcome at trial.
 I would reject the first ground of appeal advanced by the
Crown. I will, however, address that ground as the availability of
the defence of provocation may arise on the retrial. The ground
of appeal also raises an important issue relating to Crown
appeals from acquittals.
 Mr. Suarez-Noa and Ms. Cowell began dating in July 2011.
Their relationship was fractious and volatile from the outset.
They argued constantly, often by way of profanity-laced text
messaging. In September 2012, they had a baby boy. If anything,
their relationship became more strained after their son’s birth.
 Mr. Suarez-Noa and Ms. Cowell shared Ms. Cowell’s
apartment in Hamilton, Ontario. Ms. Cowell ordered the
respondent out of the apartment on two occasions in February