There's a Captain Underpants book in which the heroes put the title character under a placebo effect, which they misidentify as a "placenta effect". I had heard of the concept, but the joke went over my head, and for years I referred to the phenomenon as "the placenta effect".
A childhood belief about reading

others believed things like this
- Before the invention of the camera, everything looked like a cartoon with the quality/effect of oil painting.— MD Caruso
- When ever someone said ''read aloud'' I assumed aloud was the title of a book. Lol.— Delaney
- I used to believe in super heroes exist in the world— Kakaroto
- I used to think that if I pulled all my hair out, I would look like Colonel Klink (Hogans Heroes)— Cutto
- I thought a tidal wave was acutualy a title wave because if the wave was big enough it had its own title!— Nate
- I used to believe that Mt. Rushmore was a natural phenomenon.— LauraBee