Canon: Harry overhears Malfoy intimidating Borgin and figures out that he's been branded with the Dark Mark
Steve Kloves: Harry sees Malfoy meet a bunch of Death Eaters in Borgin and Burkes and figures out it was a ceremony to give Malfoy a Dark Mark
No but what I love about the movie version of events is that it implies that any Death Eater can brand anyone with the Dark Mark or, even better, that Voldemort was there in Borgin and Burkes and no one saw or heard him and he just popped into a shop in Knockturn Alley, tatooted a kid, and peaced out. I know I talk a lot about how Rowling (boo, hiss) was thoughtless with her world building, but she has nothing on Steve Kloves. I'm pretty sure he wrote those scripts with a crayon stuck between his toes.
