We study the diffusion of kinks, employing high-speed STM with tailor-made scan types on Au(110) and Ag(115). From direct measurements of the position fluctuations of forced kinks on Au(110), we unravel the atomistic mechanisms of the kink diffusion process. As a direct consequence of the atomic structure of a kink on this surface, a single kink displacement consists of the detachment/attachment of two atoms. The detachment energies of the two atoms differ by 72meV, resulting in the appearance of two distinct rates in the position fluctuations of kinks. We observe that kinks in close proximity to each other move by a direct exchange of atoms, and at the same time the displacement rate doubles. In addition, we measure the energy penalty when two kinks pass. On Ag(115) we study the simultaneous motion of opposing kinks. We show that the detached atoms perform a random walk along the step and have a low probability for detachment from the step. From the mean-square displacement of the kink pairs, we derive the activation energy for the emission of an atom from a kink on Ag(115).