anonymous February 17th, 2009 06:53PM  
When Jack talks about being the third man and the seventh son, he is refering to his favorite numbers (duh). He plainly says, "it was the other three that made me your third, but it was my mother who made me the seventh son!" Jack believes himself to be the all-powerful seventh son who, in mythology, either turns out to be a vampire or werewolf. In a nutshell, Jack is summing up his importance and power for this girl.