What is the burden of proving knowledge and approval in a will?

The learned professor says in his article at page 371: The burden of proving knowledge and approval is normally satisfied if the propounders prove due execution after the will was read to or by the Testator, who appeared to understand it. Thus the propounders are aided by a rebuttable presumption of knowledge and approval in these circumstances. (Citing Vout v. Hay, (1995) 1995 CanLII 105 (SCC), 125 D.L.R. (4th) 431.) However, if there are suspicious circumstances the propounders must prove knowledge and approval affirmatively. (Citing Tyrell v. Painton, [1894] P/151 at 159 (C.A.) per Davey, L.J.) They may do so, for example, by showing that the will was prepared in accordance with instructions the Testator gave to his or her solicitor.

Mr. Justice Sopinka, in Vout v. Hay, supra, stated at 488: Since these suspicious circumstances may relate to various issues, in order to properly assess what effect the obligation to dispel the suspicion has on the burden of proof, it is appropriate to ask the question, “suspicion of what”?