Balance of probabilities

The law is not my field of expertise, and I know very few legal jargons. However, I once appeared in court to defend myself and my company from a party seeking to make a quick profit. The learned judge, in deciding in favour of us, amongst others, used the phrase "balance of probabilities" in his judgement.

This post has nothing to do with the above case. But due to my fascination to that phrase by the judge, I propose to use it later... At the end of this post, I want to ask some questions; and I hope there would be some women — especially married ones — who'd be kind enough to offer an opinion.

Now imagine that a woman is aware that her husband has gone to work. She goes to bed — alone. Then an hour later, she feels a man next to her. She does not see his face — who knows, maybe it is pitch dark. That, however, does not stop her from proceeding to have an intercourse with that man. The sexual act continues, and the woman suspects nothing out of the ordinary. When it is over, the man simply leaves the room. There is of course no struggle.

And then now the husband appears in his work clothes — like he is expected to. And only now the woman realises that it wasn't her husband who she had had intercourse with. And only now she cries rape (NST).

On the balance of probabilities, without seeing the person, can a woman tell that the man next to her is not her husband? If not, would she be able to at least suspect something out of the ordinary while she is having sex with him? Would there be some habitual movements, grunts or reactions by the man during the act which would raise suspicions?

If this was an act of rape, it seems so convenient for the rapist. Everything was so calm and orderly — up to the point when the husband saw the man coming out of the room...