“It’s a great example of a twist reminding us not to rush to judgement, to look beyond the surface of things,” says Waters. “It’s also really upsetting! I think I was mildly traumatised by that story, actually, and have never quite recovered.”
Forms of this particular legend are known the world over. In a Sanskrit version dating back to around 300BC, the dog is a mongoose. But plot twists are even older than that, as pointed out by Natalie Haynes, classicist and author of Pandora’s Jar, a book, in part, about the influence of Greek myth on popular culture.
The original plot twists
“The Greeks definitely invented the plot twist,” she says. “It’s called a peripeteia – meaning a sudden reversal or change of fortune – by Aristotle in the Poetics, his study of how drama works, and he’s talking about Oedipus when he mentions it.”
Oedipus Tyrannos – Oedipus the King – is a tragedy by Sophocles which was originally performed at the Dioynsia, a big annual festival in Athens, probably in 429BC. The statute of limitations on spoilers has certainly passed on this one.
In Sophocles’s drama, Oedipus, King of Thebes, is told that, in order to lift a curse on the city, he must find the unknown killer of the previous king, Laius, whose widow, Jocasta, he has married. Oedipus had left his hometown of Corinth in order to avoid fulfilling a prophecy that he would kill his father and marry his mother. However, it transpires that Oedipus was adopted by the couple he thought were his mother and father and his real parents are – plot twist! – Laius – whom he killed without realising who he was – and Jocasta.
“So at the beginning of the play we have an unsolved murder, and by the end, we know whodunnit,” says Haynes. “It is a twist on the detective drama, because the detective finds that the criminal he seeks is… himself. This is a plot which will be used again and again – for example in the [1987 Robert De Niro] film Angel Heart.
“The moment where Oedipus sees who he really is – the man he has tried so hard not to be – is devastating. I’ve told the story of the play dozens of times to audiences and people always gasp when you get to that point. Because all the evidence is there, but they can’t believe it will be true.
“It’s perhaps worth mentioning that even though it was considered a masterpiece in its own time and now, the OT didn’t win the tragedy competition that year at the Dionysia. It came second to a set of plays by a man named Philocles. So plot twists aren’t always popular, even when they’re amazing.”
It seems those #WTF moments have been delighting and dividing audiences for at least 2,500 years.
Love books? Join BBC Culture Book Club on Facebook, a community for literature fanatics all over the world.
And if you liked this story, sign up for the weekly bbc.com features newsletter, called The Essential List. A handpicked selection of stories from BBC Future, Culture, Worklife and Travel, delivered to your inbox every Friday.