Continuity mistake: The tail number of the plane Walter is in changes. (00:30:00 - 00:31:00)
Single Point of Failure - S1-E2
Character mistake: In the letter informing him of his sister's condition it says "Nor have I scene" instead of "seen". I would not expect a medical professional to make that sort of error. (00:02:20)
Answer: A propeller sucks in from one side and pushes away from the other side.