I used to think that a cadaver was a type of knife. Maybe that was because of its similarity in sound to the last two syllables of "dagger".
A childhood belief about speaking

others believed things like this
- I used to believe Chucky would come out of my toilet, stab me with a knife, and kill me. :(
I hate Chucky. — Bijan - I used to believe that a pigeon was a type of pigAnon
- I used to think giraffes were a type of horse— Crocotta1
- i used to think that if you picked your nose you could eat it because it was a type of chicken.— nutter
- I used to believe a mouse lemur was a type of a rodent.Anon
- I thought that “selfish” was a type of fish— Enrico