horse's hooves
Refers to the hooves of a horse. Often used in set phrases like 馬蹄の音 (sound of horse hooves).
The sound of horse hooves could be heard from afar.
obsidian
Omphalius pfeifferi pfeifferi (subspecies of top shell)
Tectus maximus; top shell species
Compound of 馬 (horse) and 蹄 (hoof).