Short answer: It’s an adorable means of self-protection.
It’s called the sweet spot. That perfect place on your dog’s belly or sides that, when scratched, causes your pet’s foot to go into crazy automatic kicking mode. Every dog owner knows where to find this magical region on his or her canine, as it usually offers up unmitigated joy.
As delightful as this puppy kicking is to watch, this reaction is actually a means of self-protection for your pet. It’s called the scratch reflex, and it’s an involuntary response that exists to keep your dog safe from dangerous bugs or irritants.
Underneath certain portions of your dog’s skin, there are collections of neural pathways that are connected to the spinal cord. When these nerves are activated – either by a scratch or a tickle – they quickly send messages to the spinal cord, which then instructs the dog’s leg to kick. For some dogs, the kicking can be more pronounced depending on how much scratching they feel.
“Dogs that have allergies in particular, it tends to be really easy to illicit that scratch reflex, because the dogs are borderline itchy anyway,” says Lore Haug, a veterinarian and animal behavior expert for Texas Veterinary Behavior Services. “But when you rub their skin more, it accentuates the scratching.”
According to Haug, the scratch reflex came about as a way for animals to protect themselves against irritants on their bodies, especially invading bugs that could carry diseases. For example, if a dog has fleas running around on its skin, the insects’ itchiness will cause the scratch reflex to activate. Then, perhaps the kicking will knock some of the fleas off, alleviating the source of the itch.
It’s similar to the reflexes seen in humans, which usually exist to protect us in some way. “Let’s say you touch a hot stove, and before your brain recognizes it’s painful, the spinal cord recognizes the pain, and you involuntarily jerk your hand back,” Haug says. “If you had to wait until your conscious brain recognized something was in danger, your delay in reaction time could cause an injury or even death in some cases.”
The scratch reflex can be useful for your veterinarian to determine if your pet is suffering from any nerve damage, kind of like when your doctor tests your knee reflexes during checkups. Also, since the reflex is more for swatting away pesky bugs, it doesn’t necessarily mean your dog likes being scratched in that particular area. But of course, some dogs do enjoy a good rub on the belly. You’ll just have to pick up on cues from your pet to figure that out.