The full-on fear of clowns, or coulrophobia, is rare, but plenty of people can’t stand clowns. Why?

• Sigmund Freud identified a phenomenon he called “the uncanny.” This is when a recognizable image is distorted, but is still familiar, resulting in an unsettling juxtaposition. This is common in horror movies: a rotting face, an evil doll…or a clown. Some psychologists think that clowns fit into the “uncanny” mold: they are familiar (they’re human, they’re smiling) but they are distorted (makeup, permanent smiles).

• The mask of makeup is meant to evoke joy and happiness, but for some it creates distrust. Permanent happiness or smiling is unnatural and creepy, and it hides the clown’s humanity, which subconsciously comes across as untrustworthy.

• Similarly clowns have a long period of darkness to them that brings out the uncanny. Middle Ages jesters were mutilated if they failed to make the court laugh, their faces cut into a permanent smile with the removal of frowning muscles. (Similar to the Joker played by Heath Ledger in The Dark Knight.)

• There’s also the trope of the “sad clown,” like the one Red Skelton played on his 1960s TV show, the opera Pagliacci, or real-life clown Joseph Grimaldi. In the 1800s, Grimaldi established the modern image of the clown: white face paint with red spots on cheeks and mouth to exaggerate his face, so whole theaters could see him. He was also the first entertainer-as-celebrity, and his dirty laundry made for good gossip. In short, Grimaldi’s on-stage clowning diverged significantly from his depressed off-stage demeanor, brought on by a wife who died in childbirth, an alcoholic son, and chronic pain brought on by clowning tricks.

• Of course, coulrophobia may be attributed to murderous clowns, both fictional (Pennywise from Stephen King’s It), or real. French clown Jean-Gaspard Deburau, who performed under the name Pierrot, killed a child in 1836 as retaliation for being teased. There’s also John Wayne Gacy, who worked as a children’s party clown named Pogo around the Chicago area…until he was arrested for the murder of 33 men.