Continuity mistake: When Charlie invites Hiro over to help celebrate her birthday, the invite is almost immediately after she says "hold that thought" and walks away from his booth. But in that scene in the previous episode, Charlie was already across the room with the other townspeople when she signaled Hiro to come over.
Continuity mistake: When Hiro gives Charlie the Japanese phrase book, Charlie flips the book over to look at the back cover, then flips it frontwards again. In the next shot, she's instantly looking at the back cover again. (00:16:20)
Chosen answer: It's not been made 100% clear. It was originally assumed that he actually consumed part of the brain, but this has turned out not to be the case. Sylar has been shown all along to have an instinctive knowledge of how things work and how to fix them - this is his actual original power and the ability that made him an exceptional watchmaker and repairer. It appears that he uses a similar process when acquiring new powers - he exposes the brain of the target, allowing him to examine it and determine how their power functions. He can then apply that knowledge to his own brain, allowing him to replicate the ability in question.
Tailkinker ★