What is the test for rebutting a presumption of knowledge and approval in a will?

This presumption can be rebutted by adducing or pointing to some evidence which, if accepted, would tend to negative the knowledge and approval. This is known as the suspicious circumstances doctrine. If the presumption is rebutted, the propoundeer of the will is required to prove the will on a balance of probabilities. See Vout v. Hay 1995 CanLII 105 (SCC), [1995] 2 S.C.R. 876 at para. 27: Where suspicious circumstances are present, then the presumption is spent and the propounder of the will reassumes the legal burden of proving knowledge and approval. In addition, if the suspicious circumstances relate to mental capacity, the propounder of the will reassumes the legal burden of establishing testamentary capacity. Both of these issues must be proved in accordance with the civil standard. There is nothing mysterious about the role of suspicious circumstances in this respect. The presumption simply casts an evidentiary burden on those attacking the will. This burden can be satisfied by adducing or pointing to some evidence which, if accepted, would tend to negative knowledge and approval or testamentary capacity. In this event, the legal burden reverts to the propounder.