A Reddit user found a fossilized jawbone in their parents' newly installed travertine floor, which may be from a Neanderthal. The discovery raises questions about how many other people may have installed travertine with hominin fossils inside. Travertine is a type of limestone that can contain fossils, including those of humans, and is often used for decorative flooring and wall coverings. The article discusses the possibility of finding fossils in travertine and the importance of reporting such discoveries to the authorities.