The mischief is never managed when it comes to Harry Potter fans! They are always discovering new things about the series, even more than 20 years after J.K. Rowling's first book was published. It keeps the magic alive for all of us.
This particular theory has actually been making the rounds since at least 2015, when it was posted on a Reddit thread, but like many things on the Internet, it can take a while to reach The Rest Of Us.
Fans have been responding to the tweet above with some surprised reaction shots, although some are questioning the validity. One fan asked about the source of the killing curse hand movement. Was it from Pottermore, J.K. Rowling's official site? Whether the movement is canon or not, it looks like the tweet image on the right was picked up from Wiki.
Also, what's official in the Harry Potter world at large and what's used in the Harry Potter films is often quite different. Some fans pointed out that Voldemort (Ralph Fiennes) didn't seem to use that hand movement on screen when trying to kill Harry (Daniel Radcliffe). Also, if that's the correct hand movement, then why is it backwards on Harry's forehead?
This little detail may even be news to J.K. Rowling herself, and more on the line of a fan theory than official canon. As Digital Spy shared, Rowling explained why she chose a lightning bolt scar shape for Harry during a fan chat in 2007. At the time, she wrote, she just thought it was cool. "I couldn't have my hero sport a doughnut-shaped scar." (Sidenote: Homer Simpson should totally have a doughnut-shaped scar. The Simpsons, get on this!)
Honestly, I prefer the idea that the lightning bolt shape came from the wand movement, rather than it just looking "cool." It adds an extra layer of meaning, and we know that the Harry Potter universe is filled with deeper meanings. J.K. Rowling usually has a reason for everything, and sometimes she goes into detail on Twitter or through Pottermore.
Sometimes the revelations are things fans could've done without -- like knowing about the Hogwarts bathroom situation, pre-plumbing. But more often than not, fans are voracious about Potter intel.
Of course, J.K. Rowling is also revealing more about the Harry Potter universe through the Fantastic Beasts movies, which are all prequels to Harry Potter. J.K. Rowling is the screenwriter for all of the movies. So far, two have been released in theaters. The third movie's production was just delayed, but there are still meant to be five films in that franchise, leading up to the big duel between Albus Dumbledore and Gellert Grindelwald. That's long before Harry Potter was born, but there are plenty of new details to be learned in the films.
Fans are already reeling from the shockers of Fantastic Beasts: The Crimes of Grindelwald. J.K. Rowling promised answers are coming in Fantastic Beasts 3, which is on track to film late this year for a release date either in 2020 or 2021. Here's what's coming to theaters much sooner, right here in 2019.