The dog reflex scratch is an involuntary response that protects dogs from fleas, ticks and other sources of irritation, says Popular Science. A cluster of nerves located under the skin makes up the dog tickle spot. When you scratch your pet's tummy and hit this spot, these nerves get activated and send a message to the hind leg, via the spinal cord, to start kicking in an attempt to dislodge the source of irritation.

This doesn't necessarily mean your dog doesn't enjoy the sensation of being scratched in that spot. You can gauge your pup's level of enjoyment by paying attention to body language, Animal Planet suggests. Dogs who either don't like it or are tired of the sensation will typically try to move away. Also, a dog that frequently turns over to reveal their belly to you is signaling that they are comfortable with you and likely they are comfortable with the belly scratches you tend to give them at this time.

Where do dogs like to be petted? With few exceptions, the dog scratch reflex gets activated when you scratch or tickle certain areas of the belly and not, for example, the rump or the head. That's because the nerve clusters specific to this reflex are only located within a saddle-shaped region of the belly, known as the "receptive field of the reflex," says DogDiscoveries.com.

Do dogs like it when you scratch their sweet spot? One theory on why this nerve reflex is localized to this region is that this area is not as mobile or protected as other parts of the body, leaving it more vulnerable to parasites and other irritants.

So, why do dogs kick when you scratch them? At the turn of the 20th century, English neurophysiologist Sir Charles Sherrington became intrigued by this dog behavior and devoted considerable resources to its study.

According to his findings published in The Integrative Action of the Nervous System, the dog scratch reflex manifests in four stages:

1. The Latency Period: This is the slight delay between the time you start scratching your dog's sweet spot and the time the leg starts the "dog belly rub leg kick." The delay is caused by the time it takes for the nerve to send scratching signals up the spinal cord to the brain, and then for the signal to travel back down to the leg and activate the kicking motion.
2. The Warm-Up: This is the time it takes for the leg to really get going. The kicking motion usually starts slowly and then builds in intensity as you continue scratching or rubbing the sweet spot.
3. The After Discharge: This refers to how sometimes the kicking motion will continue after you stop scratching or move your hand away. Just as the signal to start kicking takes time to reach the leg, so does the signal that it's OK to stop.
4. Fatigue: Scratching for too long in the same spot can cause the reflex to tire out, which is why sometimes your dog's kicking slows and stops even though you keep tickling the same spot. It needs time to rest before it can become active again.

The dog scratch reflex might be amusing, but it serves a purpose in protecting your dog from pests and provides key insights into their neurological health. Whether your dog is aware of any of this, or whether they just like the sensation of getting their sweet spot scratched, one thing is almost certain — belly rubs are pretty awesome.