Factual error: The solar eclipses in the show that affected the characters' powers were referred to several times as "global events". In the episode with the second eclipse it's shown to be visible in locations thousands of kilometers away from each other at the same time. This is simply impossible, since a solar eclipse occurs when the moon passes between the Earth and the sun, casting a moving shadow that can be only about 250 km in diameter (for a total eclipse). The partial eclipse can be viewed in a much wider region, but the eclipse in the show was a total one. It's not a global event, but a local one.
Continuity mistake: Episode 3x13, "A Clear and Present Danger": When Usutu is talking with Matt in Matt's apartment, Usutu's walking stick jumps back and forth from horizontal across his shoulders, to vertical in his hands, and back to his shoulders. (00:23:40)
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 ★