It's a very contorted phrase. I struggle to think of a context in which it makes sense. I honestly don't know what it's supposed to mean. It's a mixture of subjunctive mood and passive voice, both of which detract from clarity.
You can make unclear grammatical constructions in any language. If your aim is clarity, and not obfuscation, then you just eliminate tangled grammar such as this example.
I will attempt to offer a re-phrasing with added context, though:
"The only way that anyone could have known X about her, would be if she were being observed."
(Many english speakers would substitute "was" for "were", because the subjunctive mood is rarely taught to schoolchildren in the UK. That is to say, colloquial english is generally pretty sloppy.)
If a native english speaker like me struggles with an english phrase, there's something wrong with that phrase. If I find myself constructing a phrase like that, my first instinct is that my thoughts must be unclear, because my words are unclear. I'd consider thinking again, and perhaps even re-writing an entire paragraph, just to avoid a phrase like that.
The subjunctive in German is routine and explicit. Indeed, the word "were" in my re-phrasing is pronounced in parts of northeast of england to rhyme with "bear", because it comes from the germanic subjunctive "wäre". But in general, subjunctives in English are concealed - we don't use subjunctive forms of verbs much, the listener is supposed to infer subjunctive mood from the presence of words like "if" and "would".
Twain is winding us up; after all, he was a satirist. The German language is pretty regular, compared with English. It's quite easy to learn. English must be a nightmare to learn, as a foreigner.
It doesn't sound natural to me at all; it sounds incredibly awkward to me. In a situation like that, I think people would say something like "someone would've been watching her at that moment".
(And I meant to write "would've"; the "would've had have been" was just a typo...)
But you're not; you're talking about having been being watched, something that was an ongoing process at the time (past progressive).
> And whether it's sinister or not is pretty beside the point.
People choose their phrasing because they want to convey particular connotations. So you can't just say "this is a simpler way to say the same thing" if it carries different connotations.
> I'm saying that phrasing is pretty darn unnatural English, sinister or not.
All I can say is it sounds perfectly natural to me, as a native (British/Irish) English speaker.
Of course you do. Consider "Do you ever feel like you're being watched?" versus "Do you ever feel like someone's watching you?" Both those sentences are natural English and in a certain sense they "mean the same"; nonetheless they convey a quite different feeling, and neither is a replacement for the other.
> Of course you do. Consider "Do you ever feel like you're being watched?" versus "Do you ever feel like someone's watching you?"
I was talking about in that example. I was not making a claim about every arbitrary sentence containing the phrase "being watched".
Understand that if you add enough contortions and make a sentence jarring enough, you won't get anything across without additional context. (To a human I mean. I guess I have to add that caveat because other you'll post another rebuttal about how a sufficiently strong AI would parse it just fine.)
For context, I was born and raised in Northern NJ with Jamaican parents, and have lived in Michigan for the past 10 years. I have never heard anyone use grammar like this.
I assure you the feeling is mutual :/. It really does sound perfectly normal to me. I can easily imagine e.g. Jonathan Creek saying exactly that.
"She would have had to have been watched" means she would have had to have been watched at that moment (e.g. because someone was watching the area where she did whatever it was), whereas "being watched" implies that the watching was ongoing and therefore that someone was continuously watching her at the time.