We're, of course, referring to the show's leading lady, Madison Iseman, who portrayed twins Allison and Lennon in the pilot episode so convincingly that we forgot it was one actress. And, as Madison revealed to E! News in an exclusive chat, that was completely intentional.
"We didn't want them to fall into stereotypical twin character norms," she explained. "We wanted them to feel like real people. We wanted them to be completely different. But we also wanted them to have similarities and really feel like sisters."
Mission accomplished! The first episode sees Allison and Lennon getting into an epic name-calling fight that anyone with a sibling knows too well. On making Allison and Lennon feel like two different people, Madison shared that she did a lot of journaling and background work.
"And even the physicality," she continued. "Like Lennon, she presents herself [when] she walks in the room...she reaches out, she touches people. Where Allison is much more reserved, she doesn't like to be touched, doesn't like to be looked at."
You may be thinking to yourself, why does this matter? Well, it played a big part in the first episode's jaw-dropping twist.
Unlike its predecessors, the I Know What You Did Last Summer film and book, the teens at the heart of this iteration didn't hit a stranger, rather, they accidentally crashed into Lennon's twin sister, who was walking home from a graduation party.
The panicked youths then dumped Allison's body in a cave and returned to their everyday lives—only to be stalked and harassed next summer. But, we digress.
The actual twist eventually revealed that Allison wasn't really the victim, Lennon was. Allison had been pretending to be her sister to Lennon's friends and took off in the latter's car, which is why Lennon was walking home that night.
In hindsight, it was totally obvious when Allison took over Lennon's identity: She's bad at driving, where Lennon was not. She's quiet and reserved, where Lennon was extroverted and social. Still, we gasped when we put two and two together.
Regarding the dramatic crash scene, Madison noted that it "was very emotional," as she had to not only film her death but also convey Allison's decision to change her life entirely.
"We all felt it collectively together," she concluded, "and just the atmosphere...it was heavy."
New episodes of I Know What You Did Last Summer arrive Fridays on Amazon Prime Video.