If you’re a Pokémon fan and a frequent internet user, you may have heard the term “Lavender Town Syndrome” thrown around. This cheerful-sounding condition is actually an urban legend about a creepy tune in Pokémon Red and Green for the Nintendo Game Boy. The two games were first released in Japan in 1996, and were later released in North America as Pokémon Red and Blue. The Lavender Town song supposedly made children sick when they heard it, and in extreme cases, it drove them to commit suicide.

Pokémon Red/Green eventually takes players to Lavender Town, a small village that serves as a Pokémon graveyard. It’s a disturbing place for a number of reasons.

For starters, Pokémon are generally cute and furry creatures, so we don’t think about their mortality unless we’re forced to (when Pokémon fight, they just “swoon” each other). Lavender Town is also home to Pokémon Tower, a creepy structure haunted by the ghost of a Marowak who was killed defending his baby from Team Rocket. Finally, Lavender Town’s theme music is a little creepy, and it’s on this melody that Lavender Town Syndrome is based.

According to legend, Lavender Town Syndrome began when about 100 Japanese children, aged 10 to 15, jumped to their deaths, hanged themselves, or mutilated themselves a few days after the release of Pokémon Red/Green. Other children reportedly complained of nausea and severe headaches.