What is the testatrix's mental state?

The decision of Cullity J. of this court in the 2001 judgment, Scott v. Cousins [2001] O.J. No. 19, is a goldmine of legal principals dealing with testamentary capacity, the requirement that a testator understand what is being done, mental disabilities, confused state of mind, undue influence and burdens of proof. In that case at paragraph 99, Cullity J. said, I am not satisfied on a balance of probabilities that … [the testatrix] was capable of appreciating the claims and worthiness of the persons who were her closest relatives and for many years had been the intended residuary beneficiaries of her will, and of making a rational decision to revoke the bequests to them in her previous will.