Homenum revelio

Homenum revelio is a spell which reveals any human presences within a building. It may be related to the spell Specialis revelio which reveals special qualities in an object, such as intelligence, enchantments, or hidden words and pictures. When recited properly, the spell indicates a body by a marker, the appearance of which is yet unknown, but which can be felt by the target person as something "swooping" low over him or her.

Etymology
Homenum revelio derives from the Latin homo and revelare, meaning "human; person" and "to reveal", respectively. The incantation itself is a variation of "hominum revelo", the proper Latin for "I reveal a person".