My mother did this when she was young.
She was doing the dishes and complaining to her father that she couldn't get a pan clean, so he told her to put a little elbow grease into it. She in turn searched the cupboards for the elbow grease can while he laughed his but off. she had no idea it wasn't a cleaning product
A childhood belief about around the house

others believed things like this
- I used to think that "elbow grease" was an actual product of kitchen or surface cleaner.— Carrie
- I always thought that "elbow grease" was a type of lubricant until about 2 years ago. I'm 19.— Erika
- When I was very small. by older brother told me that if I "Kissed my own elbow, I would turn into a boy."Anon
- I called every body part my elbow. For example if my leg hurt I would say my elbow hurt.— Kady
- I used to believe that if I could kiss my elbow that I would turn into a girl (the opposite sex).— Rusty
- My sister told me that if I could kiss my elbow I would change into a boy. I never disproved her on this.— Aussie