The rider tugged on the of her horse to make him slow down. reinsranesrainsreigns

The answer is reins. This is a lengthy, thin leather strap attached at one end to a horse's neck, usually used in pairs by which the rider or driver leads a horse or other animal by pulling so as to exert pressure on the bit while horse-riding or driving.

The main idea exclaims how everyone has mercy, even the greatest of kings yet have mercy.