When a coin is tossed, it doesn't land heads exactly 50% of the time. Research shows a slight bias, primarily because a coin is more likely to land on the side that was facing up when it was tossed, with about a 51% chance for that initial side. While the 'heads' side often has a more intricate design and is slightly heavier, this weight difference has a more pronounced effect when a coin is *spun* (leading to more tails) than when it is *flipped*.