Nail prick
Nail prick or quicking occurs in a horse if the sensitive hoof structures (usually the sensitive laminae) are penetrated by a horseshoe nail being driven through the hoof wall while shoeing. The nail creates a wound on the inside of the hoof wall.
A close nail or a nail bind is the placement of a horseshoe nail so close to the sensitive structures inside the horse's hoof that it causes discomfort to the horse. The nail is not necessarily placed in the sensitive structures itself, but creates a pressure on the quick of the horses hoof.