Credit: Clay Enos/Warner Bros

It’s been six months since Batman v Superman: Dawn of Justice arrived in theaters and nearly three months since the film’s extended Ultimate Edition was released, but there’s apparently still more to be discovered about the superhero showdown.

The film’s set photographer, Clay Enos, confirmed a new Easter egg that explains why (spoiler alert) Batman was able to weaken Superman during their titular battle by firing kryptonite gas at the Man of Steel.

Couldn’t Superman have used his X-ray vision to see what was in the Dark Knight’s canisters? Well, as pointed out by an eagle-eyed viewer (via Screen Rant), the canisters Bruce Wayne/Batman used have “Pb” — the abbreviation for lead in the Periodic Table of Elements — etched on them.

Lead, as Superman fans know, can block the superhero’s X-ray vision. When asked by another fan if that was intentional on director Zack Snyder’s part, Enos affirmed that it was. “Nothing happens by accident in Zack’s movies,” he tweeted.

The next film to arrive in the DC movie universe will be the Gal Gadot-starring Wonder Woman, in theaters June 2. After that, Batman and Superman will be back with the rest of their heroic counterparts for Justice League, which arrives Nov. 17.

Batman v Superman: Dawn of Justice
  • Movie
  • 151 minutes