Neatsfoot Oil
Neatsfoot oil is a yellow oil rendered and purified from the shin bones and feet (but not the hooves) of cattle. “Neat” in the oil’s name comes from an Old English word for cattle.[1] Neatsfoot oil is used as a conditioning, softening and preservative agent for leather.
Wikipedia.org, accessed on 28 June 2019
Neatsfoot oil is applied to leather knife sheaths to preserve and beautify the leather.