A witnessed fall is a meteorite whose arrival on our planet was seen and documented by credible observers. Witnessed falls are very rare, and are highly prized by collectors. Slickenside is a geological term used to describe a polished face on a rock, created when two adjacent masses move against each other for a prolonged period of time. While fairly commonplace on earth, slickenside is extremely rare in meteorites, and shows us that some of the processes at work on astral bodies such as large asteroids, are very similar to those which occur on our home planet Earth. Zag and Carancas are two of the very few meteorites which show slickenside, and the dark surfaces are sometimes mistaken for fusion crust.