What constitutes an "unusual danger" to a person who is in possession of an unoccupied building?

Such “unusual danger” may be the actions of a third party, lawfully on the premises, which were known or ought to have been foreseen by the occupier as constituting a danger; Hanes v. Kennedy, 1941 CanLII 6 (SCC), [1941] S.C.R. 384.

Estey, J., concluded in the Cuellet case (supra), at p. 433: Even if it be assumed that the mere presence of the defendant in the beverage constituted an ‘unusual danger’, it must be of such a nature that it was known to the defendant hotel or its employees, or ought to have been known. I do not think that the evidence establishes knowledge on the part of the defendant hotel of a propensity by the defendant to physically attack another patron in the beverage room, nor were facts given from which an inference could be drawn that the defendant hotel or its employees should have known of such a propensity in the defendant. Therefore, I do not think that liability can he attached to the defendant hotel on the basis of the principle set out in Indermaur v. Dames, supra.