A jaw on the floor

The idiom describing shock or astonishment is familiar to everyone, but in this case a jaw is literally on the floor.

"My parents just got their home renovated with travertin stone. This looks like a section of mandible. Could it be a hominid? Is it usual?"

That question was posted by a dentist at the Fossils subreddit, where there are numerous informed replies explaining that this could indeed be a human jawbone (image cropped for emphasis).   There is a detailed scientific explanation at John Hawks (via Neatorama):

Travertine is a limestone that forms near natural springs. Spring water that emerges from lime-rich bedrock often carries a high concentration of dissolved calcium carbonate. When the water evaporates or cools—especially near hot springs—this calcium carbonate precipitates as rock and may form very large deposits around the spring. Travertine has an interesting internal texture when polished, and often has color bands and inclusions of calcite crystals, which make it an appealing choice for decorative flooring or wall covering.

Travertine also commonly includes fossils. Many are fossil inclusions of algae, plants, and small animals—especially molluscs and crustaceans—that live within the spring water. Much larger animals may be found and humans are no exceptions: Several well-known hominin fossil discoveries are from travertine deposits. Most of these discoveries have happened because of quarrying of the travertine deposits for use in construction.

For example, the Steinrinne site is on a terrace of the Wipper River near Bilzingsleben, Germany. The site was quarried from the Middle Ages onward into the twentieth century. Naturalists took notice of the fossils there in the nineteenth century, and straight-tusked elephants, woolly rhinos, and macaques all occur in great numbers, dating to an interglacial period sometime between 470,000 and 280,000 years ago...

Quarries rough-cut travertine and other decorative stone into large panels, doing basic quality checks for gaps and large defects on the rough stone before polishing. Small defects and inclusions are the reason why people want travertine in the first place, so they don't merit special attention. Consumers who buy travertine usually browse samples in a showroom to choose the type of rock, and they don't see the actual panels or tile until installation. Tile or panels that are polished by machine and stacked in a workshop or factory for shipping are handled pretty quickly.

What this means is that there may be lots more hominin bones in people's floors and showers...

It isn't a crime scene. But depending on your state or nation of residence, laws governing discovery of human remains on your property may be complicated and having the paperwork in order with the police, sheriff, or coroner is the first step for most investigations...