Up until I was about 8 years old, I believed that all dogs were male and all cats were female. Then, when my friend got a dog for her birthday, I suggested she name it Grover (for whatever childish reason). She looked at me funny and said, "But she's a girl!" :) There goes that theory!
A childhood belief about cats and dogs

you weren't the only one
215 of you believed this
- I used to believe that cats were all female and dogs were all male.— Rachel
- that cats were only girls and dogs were only boys. I definetly didn't get the whole reproducing thing yet.— Jamie
- i used to believe a dog was the male version of a cat.Anon
- I believed that all cats were female and all dogs were male. — Biologically confused
- i thought cats were girls and dogs were boys. Anon
- i used to believe that all cats were female and dogs were male!Anon