Silly question. Since I have been watching Alien so many times lately I began to wonder: does Dallas knows Ash is an android? Ash is the only person on the ship that Dallas listens to and sometimes takes orders from. When Ash says the facehugger has to go back Dallas accepts that decision in the face of everything that's happened. Dallas as the captain is the only one to have access directly to Mother so its not unreasonable to think he might know an android is aboard also. He seems to know that Ash equals the company.