Thanks to one Reddit user, the mystery of how Kevin’s parents accidentally left him at home has finally been explained.
In the beginning of the movie, Kevin and Buzz accidentally spill milk over everyone’s plane tickets and passports. Kevin’s dad quickly cleans up the mess and throws the wet napkins into the trash. However, the camera lingers over the garbage can for a few seconds. Upon closer inspection, it's obvious that the trash includes Kevin’s plane ticket, which his father accidentally threw away.
When the family arrives at the airport and begins to board the plane, an airline employee simply collects the McCallisters’ tickets instead of matching names with people, which means that without a ticket for Kevin, no one would notice his absence.
Some of the movie’s mysteries still remain unsolved, like the explanation for Old Man Marley’s gruesome injuries. Though the creepy old neighbor did save Kevin’s life, he didn’t make great strides toward putting Kevin at ease, especially after slamming his bloody hand onto a countertop in front of the kid.
Skeptics have also pondered over an explanation for the pizza boy’s silence after believing he was almost murdered. Since the McCallisters’ TV clearly convinces passerby that semi-automatic gunfire is actually coming from inside the house, it seems unrealistic that the pizza delivery guy wouldn’t report the gunfire to police.