Ambergris.

Ambergris is produced in the gut of the sperm whale and expelled into the sea, where it floats for years, oxidising under sun and salt until it transforms from foul black tar into pale grey waxy lumps that smell of marine air, warm skin and old wood.

Today it is mostly replaced by synthetics like Ambroxan, but a few houses still source naturally beach-cast ambergris — never harvested from whales.