Coming in hot like a meteor from across the cosmos, the trailer for Captain Marvel spotlights Brie Larson as the space-faring superhero primed to take down Thanos in 2019.

But one moment in the trailer is just begging for an explainer: Why on Earth does Captain Marvel punch a sweet elderly woman on a bus?

There’s actually a very good reason why Captain Marvel appears to commit assault in public: That old lady is probably, definitely, a Skrull.

WTF Are Skrulls?

Introduced way back in issue #2 of the very first volume of Fantastic Four by by Stan Lee and Jack Kirby, the Skrulls are an alien race engaged in a never-ending war with the Kree, the alien race seen in 2014’s Guardians of the Galaxy. (Lee Pace’s Ronan the Accuser was a Kree extremist.)

A particular subspecies of Skrulls, known as Deviants, are distinct for their ability to shape shift and change their appearance. In an ancient war, this came in handy for Deviants, allowing them to presume dominion over the two other Skrull species, the Prime and the Eternals.

In 2008’s Secret Invasion by Brian Michael Bendis and Leinil Yu, Skrull ruler Queen Veranke led an invasion of Earth using her species’ ability to change as their chief infiltration tactic. It was revealed that Skrulls had been hiding in plain sight for quite some time, posing as Marvel heroes like Spider-Woman, Elektra, Hank Pym, and even Mar-Vell, the original Captain Marvel.

Secret Invasion Captain Marvel
Cover of 'Secret Invasion' #1, illustrated by Gabriele Dell'Otto.

Decades after their comic book debut, Skrulls are finally invading the Marvel Cinematic Universe. And it appears they’ve already kicked off their invasion of Earth, judging by images seen in the trailer.

So rest assured that Carol Danvers isn’t punching an old lady for no reason. She’s trying to save the world.

Captain Marvel hits theaters on March 8, 2019.