The first episode of the war drama Over There includes a grisly scene in which an Iraqi insurgent’s legs keep running after the top half of his body gets ripped off by a grenade. Slate’s Dana Stevens wonders whether this could really happen: Can your legs keep running if your torso gets blown away?
Maybe, but only for a few steps. The most interesting data on this topic comes from studying felines. Research that began in the early 20th century shows that a cat with a severed spinal cord can be induced to move its paws in rhythmic steps. A cat will even scamper along on a treadmill right after having its brain cut off from the rest of its body.
Cats walk using a neural circuit that’s located in the spinal cord. Once the higher levels of the nervous system—the brainstem and the brain—activate this circuitry, the cord makes the cat go. Meanwhile, the cat’s brain uses sensory information from its limbs and eyes to control its speed and to avoid obstacles.
Less is known about how the human nervous system controls walking. People who lose all feeling in their legs because of spinal injuries can experience sudden, rhythmic stepping motions in certain postures. Newborn babies will also step spontaneously if they’re held upright and moved across a table—even those born with severe brain deformities. Higher-level control of locomotion seems to be more important for humans than for cats. Even if human walking were controlled by the spinal cord, the brain would still be necessary to initiate movement and control balance.
So, could a disembodied pair of legs run a few feet before falling to the ground? It’s not impossible. A major spinal injury creates a sudden surge in neural activity, which could turn on a spinal circuit that controls rhythmic stepping. You wouldn’t even have to be in midstep when it happened—an injury could conceivably send a pair of legs running from a standing start. But without a brain to oversee the movement and maintain balance, the legs would quickly topple over.
In Over There, the insurgent gets blown in two just above his jeans, and there’s no sign of an intact spinal cord peaking out above the waistline. This scenario makes post-traumatic stepping very unlikely, since the parts of the cord that control the legs would have been destroyed. Without the right spinal circuitry, disembodied legs can’t go anywhere.
The best data, of course, come from the trenches. A couple of Slate readers referred Explainer to the World War I autobiography of Pvt. Bill Green, as referenced by the historian Pierre Berton. According to Berton, Green watched as a “headless corpse, blood spouting from the severed arteries, actually took two steps forward before toppling in the muck.”
Explainer thanks Keir Pearson of the University of Alberta and readers Ken Clasper and Tyler Hargreaves for the Berton reference.