When I was little my great-aunt had a storage shed out back turned into a home for tons of stray cats. To get us to wash our hands after we played with them, Aunt Ruby would tell us "If you swallow a cat hair, it'll turn into a worm in your stomach." I knew that dogs and cats sometimes got worms so this made perfect sense to me. I believed it well into high school.
A childhood belief about cats and dogs

others believed things like this
- My sister and I thought cats and dogs were the same animal, the dogs were male and the cats were female.— Paul
- I used to believe all dogs were male and all cats were female. I still call dogs "boy" and cats "girl." — Kelly F.
- I use to believe that cats and dogs were the same species; cats were girls and dogs were boys.— poopcrystals
- Looking back at it, the belief that dogs eat cats is a pretty funny idea. I used to believe it myself.Anon
- I believed that all cats were female and all dogs were male. — Biologically confused
- When I was a little girl, I believed that all cats were girls and all dogs were boys. :)— Mary Ellen