I was told in Sunday school that males had one rib less than females and the reason was that Eve was made from Adam's rib.
Before ultrasound was able to determine sex of a fetus, I suggested to my parents that an x-ray could be taken of the fetus and count the ribs. Naturally they thought that was funny and so I never forgot the humiliation.
A childhood belief about general

others believed things like this
- I thought that all cats were the females, and that the dogs were the males.— opps guess not
- My cousin thought ribs at restaurants were people ribs.Anon
- I thought the expression "so funny I forgot to laugh" was literal instead of sarcastic— Not so funny after all
- I thought that Count Dracula was the count from Sesame StreetAnon
- that the money I gave at sunday school would go straight to God.— christine
- I thought baby back ribs were from actual babiesAnon