Here’s a haunting challenge: If you had to prove you were a human user online by checking all images of gargoyles (as opposed to grotesques), which ones in this grid would you choose? (Answers below).

First, you’d need to know the difference. What makes a gargoyle a gargoyle?

While the term is often applied to any type of fantastic figure adorning a building, there’s an important caveat: gargoyles serve as downspouts, while grotesques don’t.

Originally, gargoyles functioned as decorative disguises for roof drainage, directing water away from facades like that of Notre Dame Cathedral in Paris. Gargoyles and grotesques also served as part of a dense decorative program meant to instruct—and terrify—the illiterate masses.

In our work restoring New York’s buildings, we’ve encountered many gargoyles and grotesques—surprising and sinister figures glaring down from parapets and facades. They menace (or occasionally welcome) our team with leering looks wrought in terra cotta and stone. And not just on Halloween, but every day of the year.

*The top left (from City College’s Compton-Goethals Hall) and bottom right (from Sheffield-Sterling-Strathcona Hall, Yale University) images are proper gargoyles.