Many people assume that they perceive the world as it actually is—as if eyes and ears were windows that allow us to access an objective reality. But perception is not an accurate reflection of an externally existing world.

“In fact,” the neuroscientist Anil Seth says, “perception and hallucination have a lot in common. You could say that we’re all hallucinating all of the time, and when we agree about our hallucinations, that’s what we call reality.”

In an animated video produced by Carolyn Merriman of the Future of StoryTelling and animated by Steve West of Lazy Chief, Seth explains how the brain operates on implicit beliefs accumulated over thousands of years of human evolution. These, he explains, are what “turn the raw material of sensory data into our projected perceptual realities.”

Most of the time, we can all agree on these perceptions. But sometimes this consensus breaks down, such as in the case of the Internet phenomena of the white-and-gold versus black-and-blue dress or the “laurel” versus “yanny” audio clip. These are stark reminders of what Seth describes as the “neurological guesswork that happens behind the scenes.” In these moments, the curtain is lifted on the theater—not the window—of our reality.

“Our brain is doing its best to make sense of ambiguous sensory input,” Merriman told The Atlantic. “In some ways, our perception of the world is just the story our brains are telling us based on the sum of our senses.”

The mind’s ability to create this congruous narrative of reality continues to awe Seth. “I am inspired by how such a small biological machine inside my head—inside the head of everyone—can create such a rich inner universe for each of us from the raw material of sensory signals,” he told The Atlantic. “This is a monumental achievement, one that is far outside the scope of any artificial machine or computer we’ve ever constructed.”

He recited his favorite lines of poetry, from Emily Dickinson’s 1924 poem “Part One: Life”:

The brain is wider than the sky / For, put them side by side, / The one the other will include, / With ease, and you beside.