When I take Luna, my dog, on a car trip she lays down and sleeps in the back seat. This is not normal behavior. Normally, dogs are thrilled to be in the car and want to stick their heads out the window and take it all in. They seem to love it! But why?

As you would guess, sticking his or her head out the window is a sensory bonanza for your pup. “It’s a highly stimulating experience for them—the scents, the feeling of the wind, all of the sights that they can see,” explained veterinarian Dr. Cathy Meeks. 

Dogs have more than 100 million sensory receptors in their noses (compared to the 6 million humans have). The part of their brain that’s devoted to processing scents is also about 40 times larger than that of a person’s. When dogs exhale through the slits in their nostrils, the air swirls around and introduces a whole host of new, interesting odors. Sticking their heads out of car windows (or any open windows) lets them really soak in all the smells of the outdoors. 

The sights are exciting, too. Dogs may see fewer hues than humans—and are often near-sighted—but they can spot moving objects better than stationary ones. The animals have 10–20 times greater motion perception than people. That means the landscape flying by in a car may be blurry to our eyes, but it’s likely much sharper for a canine passenger. 

Riding in a car may bring joy to many dogs—and their owners, who get to witness the animals’ faces goofily flapping in the wind—but it doesn’t come without risks. Flying debris, close-passing vehicles, and branches and poles are all dangerous threats. Smaller objects, like pebbles, dirt, flying insects, or other airborne particles, could also cause trouble; they may end up in a dog’s eyes, leading to injury or infection. 

And if the driver suddenly stops or swerves when a canine passenger has his or her head poking out a wide-open window, the animal could be thrown out of the car, or they could potentially hurt themselves by accidentally rolling up the window with their paws and squishing their head, chest, or neck. They may even attempt to jump out of the car to chase something—or they could lose their balance and fall while attempting to launch.

So, let the dog live their best life and enjoy the adventure, but be careful and keep watch on the situation. Because not all dogs like to lay down and sleep in the back like Luna does!