Why Do Dogs Shake Their Legs When You Pet Them?

The scratching exhibited by dogs while being petted is a reflex called the scratch reflex. This reflex is so reliable that veterinarians can actually use it to test for certain neurological problems. The scratched area that elicits the response can vary from dog to dog, but the belly, chest and sides are the most likely locations to activate it. The reflex may occur because scratching makes the dog feel like she has an itch, or it may be a lingering defensive reflex and not the result of any particular physical sensation.

The scratch reflex remains active even in very sick dogs, indicating that it is indeed a reflex. Spinal cord injuries, however, can cause a dog to lose sensation or cause the brain to process signals incorrectly and affect this reflex. Thus veterinarians sometimes scratch dogs to test for spinal cord injuries or malfunctions.

Not all cases of kicking are caused by the scratch reflex. If the kicking is only periodic, your dog may be trying to redirect the location of your scratching or indicate that you've hit a sore spot. Occasionally your dog may kick her legs when she has an itch she can't reach on her leg or another part of the body.

The scratch reflex is a completely harmless reflex, and the degree of kicking doesn't correlate with health as long as the dog kicks. Dogs can, however, inadvertently harm their owners with excessive kicking by scratching them, so ensure your dog's nails are kept trimmed. If your dog has any joint problems, such as hip dysplasia, avoid scratching her while she's standing up. The scratch reflex could cause her to fall and injure herself.