On Twin Earth, a brain in a vat is at the wheel of a runaway trolley. There are only two options that the brain can take: the right side of the fork in the track or the left side of the fork. There is no way in sight of derailing or stopping the trolley and the brain is aware of this, for the brain knows trolleys. The brain is causally hooked up to the trolley such that the brain can determine the course which the trolley will take.