Narrator: Imagine a school gymnasium. Inside, an elephant detects the faint, lingering scent of a mouse that passed through hours ago. A rattlesnake, blind to the room's colors, instead sees a glowing heat-map of the creatures within it, tracking the warm-blooded mouse with deadly precision. A bumblebee ignores the plain yellow walls, captivated instead by the ultraviolet patterns on a flower placed in the corner, patterns that are completely invisible to a human. A bat, plunged into sudden darkness, navigates not by sight but by sound, painting a picture of the room with the echoes of its own high-pitched calls. All these creatures, and a human named Rebecca, share the exact same physical space, yet they inhabit fundamentally different worlds. Each is enclosed in its own unique sensory bubble, perceiving only a tiny fraction of the immense reality that surrounds them.

This is the central puzzle explored in Ed Yong’s groundbreaking book, An Immense World: How Animal Senses Reveal the Hidden Realms Around Us. The book is a journey into these hidden realms, a guided tour of the unique sensory worlds—the Umwelten—of the creatures with whom we share our planet. It reveals that the world we perceive through our human senses is not the world, but merely one version of it.

Narrator: For humans, the world is primarily a visual and auditory place. But for many animals, reality is constructed from a universe of chemical signals. The book dismantles the human-centric view of the senses by first plunging into the world of smell and taste. Consider the dog. Its sense of smell is not just a more powerful version of our own; it is a fundamentally different way of experiencing the world. A dog’s nose is a marvel of engineering, with a separate respiratory path that allows it to sniff continuously, creating an uninterrupted stream of olfactory information. As dog cognition expert Alexandra Horowitz describes, a dog is in a constant state of "olfactory exploration," reading the history of a place—who has been there, what they felt, where they went—from the lingering molecules in the air. For a dog, a walk around the block is like reading the morning newspaper, rich with stories and updates invisible to its human companion.

This chemical world is even more foundational for social insects. The clonal raider ant, for example, lives in a world built almost entirely of pheromones. These chemical messages dictate every aspect of its life, from identifying nestmates to following trails and caring for young. In one experiment, when scientists disabled the gene responsible for smell in these ants, the colony fell apart. The "anosmic" ants became un-ant-like; they wandered aimlessly, ignored their young, and failed to recognize their own kin. As the great biologist E.O. Wilson noted, the ant world is a "tumult, a noisy world of pheromones," a bustling metropolis of communication that is entirely imperceptible to us.

Narrator: Vision, a sense humans prize above all others, is no more universal than smell. An Immense World reveals an astonishing diversity in how animals see. The jumping spider, for instance, has eight eyes, each with a different job. Two large, forward-facing principal eyes provide high-resolution, color vision, moving like tiny, internal telephoto lenses to scan a scene. Its other, secondary eyes are motion detectors, providing a blurry, wide-angle view that alerts the spider to any potential prey or threat. It has effectively separated the tasks of "what" and "where" into different sets of hardware.

The perception of color is even more subjective. Humans are trichromats, building our world from three primary colors: red, green, and blue. But most mammals, including dogs and horses, are dichromats, seeing a world of blues, yellows, and grays. This is why orange safety markers at a horse race are nearly invisible to the horses they are meant to guide. Birds, however, are tetrachromats. They have a fourth color cone for ultraviolet (UV) light, unlocking a dimension of color humans cannot imagine. They see non-spectral colors like UV-green and UV-yellow. In a remarkable experiment, scientist Cassie Stoddard proved that hummingbirds could easily distinguish between two feeders that looked identical to humans, because one was a pure color and the other was a mix of two colors that included a UV component. For a bird, the world is painted in a far richer palette, a "thermonuclear bomb of light and beauty" that we are blind to.

Narrator: Beyond the familiar senses, animals have evolved abilities that seem almost supernatural. The sense of touch extends far beyond simple contact. Treehoppers, tiny insects that live on plants, communicate not through airborne sound but through vibrations sent through the stems and leaves. Biologist Rex Cocroft allowed his colleague to listen in with a special microphone, revealing a hidden soundscape of chirps and moos that were completely silent to the naked ear. Similarly, a sand scorpion hunts by detecting the minuscule seismic waves made by its prey walking across the desert floor, using the sand itself as a giant web.

Sound, too, takes on different forms. While humans are confined to a narrow band of frequencies, bats and dolphins use ultrasound for echolocation, emitting high-frequency calls and interpreting the echoes to build a detailed, three-dimensional image of their surroundings in complete darkness. Conversely, elephants and whales use infrasound—frequencies too low for humans to hear—to communicate over vast distances, their rumbles traveling for miles through the ground or ocean. The book also explores senses with no human equivalent at all. Sharks and platypuses can detect the faint electric fields generated by the muscles of their prey, a sense called electroreception. And sea turtles and birds navigate their epic migrations by sensing the Earth’s magnetic field, using an internal compass that science is only just beginning to understand.

Narrator: Perhaps no creature better exemplifies the book's core message of humility than the mantis shrimp. With eyes that are arguably the most complex on the planet, it was long assumed to be a connoisseur of color. It has at least twelve classes of photoreceptors, compared to our three. Four of these are dedicated just to UV light. For years, scientists speculated about the psychedelic visual world it must inhabit.

However, when researcher Hanne Thoen finally tested their ability to discriminate between colors, the results were shocking. The mantis shrimp was terrible at it. It struggled to tell apart colors that are easily distinguishable to humans. The solution to this paradox is a lesson in evolutionary ingenuity. Instead of comparing inputs from its many photoreceptors to perceive millions of subtle shades, as the human brain does, the mantis shrimp appears to use a radically different system. It may recognize colors instantly, without complex processing, by seeing which of its twelve photoreceptor channels is most strongly activated. Its visual system acts less like a camera and more like a barcode scanner, sacrificing nuance for speed—a critical advantage for a creature that makes its living with one of the fastest and most powerful punches in the animal kingdom. The mantis shrimp is a profound reminder that more complexity does not mean a more human-like experience.

Narrator: The final, sobering insight of An Immense World is that these rich sensory landscapes are under threat. Human activity is flooding the planet with sensory pollution. Artificial light at night disorients migrating birds and leads newly hatched sea turtles to wander inland to their deaths instead of toward the moonlit sea. The constant drone of ship engines, seismic surveys, and industrial activity fills the oceans with noise, masking the calls that whales use to find mates and the subtle sounds that fish use to locate reefs.

This sensory pollution effectively blinds and deafens other animals, severing their connection to the environment and to each other. It shrinks their Umwelten, forcing them to live in a muted, confusing, and impoverished world. Protecting a species is not just about preserving its habitat; it is about preserving the integrity of its sensory environment. It requires us to save the quiet and preserve the dark.

Narrator: The single most important takeaway from An Immense World is that there is no single, objective reality. There is only a collection of subjective, perceived realities, each shaped by the unique sensory toolkit of the organism experiencing it. Our own human experience, which we so often mistake for the complete picture, is just one sliver of an immense and wondrous whole.

The book is more than a cabinet of curiosities; it is a profound call for a new kind of empathy. It challenges us to move beyond our own sensory bubble and consider the world from other points of view. The ultimate impact of Ed Yong’s work is to ask a critical question: As we continue to shape the planet, will we do so with only our own Umwelt in mind, or will we learn to consider the countless other nations of animals, "caught with ourselves in the net of life and time," and strive to protect the hidden, sensory worlds that are as vital to their existence as our own is to us?