At first glance, the puzzle looks incredibly simple.

Four glasses labeled A, B, C, and D appear to contain nearly identical amounts of water. But inside each glass sits a different object — and that tiny detail changes everything.

The challenge sounds easy:
Which glass actually contains the most water?

But as thousands of people discovered online, the answer depends on whether you focus on appearance… or physics.

Glass A contains a paperclip.
Glass B holds a baseball.
Glass C contains an eraser.
Glass D has a wristwatch.

Most people immediately judge the puzzle based on water level alone. Since all four glasses appear equally full, the brain instinctively assumes the amount of water must be roughly the same.

That’s where the trick comes in.

The key to solving the puzzle is understanding displacement.

Every object placed inside the glass takes up space. The larger the object, the less room remains available for actual water.

That means the correct answer is Glass A.

Because the paperclip is the smallest object, it displaces the least amount of water. In other words, Glass A contains more real water than the others, even though the surface levels appear similar.

Meanwhile, the baseball in Glass B takes up a huge amount of space, meaning there’s actually far less water inside despite what your eyes initially suggest.