The chip is inserted under the skin between the shoulder blades of a cat or dog, in much the same way that a vaccine is administered. (ypsivet.com)
For dogs up to 20 lbs, apply to skin on back between the shoulder blades. (all-about-puppies.com)
A tiny microchip, about the size of a grain of rice, is placed right underneath the skin in between the shoulder blades. (orovilleveterinaryhospital.com)