Plants seem so passive. Tree branches bow to the wind, losing their leaves. Lettuce just sits there as snails help themselves to a free salad bar. And grass lets everyone walk all over it.

But all that apparent listlessness is deceptive. In truth, plants are incredibly active members of their communities. Plants move on their own all the time—creeping, digging, reaching, blooming. However, most of the action happens too slowly for our eyes to see unaided. In his 1995 documentary series The Private Life of Plants, David Attenborough and his crew created beautiful time-lapse videos to showcase plants' hidden mobility. Climbing jungle vines race one another up tree trunks, stretching towards the sunlight. The thorny bramble whips from side to side, shoving competing plants out of the way to expand its territory.

» View a slideshow of the plant kingdom's most unusual talents

A spindly orange vine known as dodder is a particularly striking example of dynamic plant life. Dodder is a parasite—it lives off of other plants. Instead of waiting around for a suitable host, the vine hunts one down. Conseulo De Moraes of Penn State University planted a young dodder near a tomato plant and continuously filmed the pair for several days. Her time-lapse video reveals a growing dodder flailing around, tasting the air like a snake, until it finally brushes the tomato's stem and begins to encircle its victim. Eventually it would sink tiny nozzles into the tomato plant to suck out vital juices.

De Moraes discovered something surprising about the dodder: it can smell. The vine sniffs out its hosts, growing toward telltale chemicals released by its neighbors. And it is picky. Dodder prefers juicy tomato plants to slender wheat and healthy plants to sick plants. Tel Aviv University biologist Daniel Chamovitz discusses dodder and many other fascinating plants in his upcoming book, What A Plant Knows, an excerpt from which appears in the May issue of Scientific American.

Dodder is hardly the only plant whose mobility and abilities would surprise most people. The plant kingdom is full of unusual talents that are more common than biologists first realized. The Venus flytrap is only one of several different kinds of carnivorous plants that have developed astonighing ways to catch and digest insects and other small animals. Almost all plants have evolved chemical defenses against herbivores and many plants recognize when their neighbors are under attack, preparing for battle themselves. Alpine buttercups track the sun's arc over the course of a day to keep their blossoms warm and appealing to heat-seeking pollinators. The telegraph plant swivels its leaves to maximize exposure to sunlight, adjusting so quickly that you can see the leaves moves in real time. Some plants may even distinguish between family and strangers, sharing resources only with the former.

» View a slideshow of the plant kingdom's most unusual talents

Like most organisms, plants sense and respond to their environments. To appreciate just how sensible plants are, we have to look at the world—or even smell the world—from their perspective