What is the twist in The Box?

I'm curious to know, what exactly is the unexpected turn of events, or the "twist," in the movie "The Box"? I've heard it's a suspenseful thriller, but I'm eager to understand the key moment that shifts the narrative and keeps viewers on the edge of their seats. Could you elaborate on the twist and how it impacts the overall story? I'm intrigued by how such a moment might challenge our expectations and keep us guessing until the very end.