This isn't my belief, but a few years ago my best friend made her little brother believe that if you ate only one food for an entire week (for example, apples), that your farts would smell like apples.
He never got to test the theory because there's no way a parent would let their child eat only one food for an entire week!
A childhood belief about farting

others believed things like this
- i used to think mashed potatos were made from apples becouse they were the same color(i was a very slow child)— apples and ornges
- i used to associate the word appetite with apples, if you ate apples, you had an appetite. — elly
- I was told that your belly button is where you put salt when you eat apples in bed.— Shurnuff
- Once my mother told me that if i ate 2 apples in a day, i would automatically get diahrreah!Anon
- I used to believe that if you ate the pips in apples a tree would grow inside your stomach.— QueenB
- i used to believe that if you swallowed the seeds from apples, trees would grow out of your ears!— Scott Davenport