When I was in High School Chemistry, my teacher showed us a cow magnet. Apparently farmers make cows swallow strong magnets to attach to other metal things they accidently eat, like nails. This somehow prevents damage.
When he told us about them, he said that they sit in cows stomachs, and when the farmer wants to cows to come back into the barn, he turns on a giant electromagnet and the gentle "pull" in the cows' stomachs makes them go back in...
..apparently, he was joking.
A childhood belief about general

others believed things like this
- I used to believe chocolate milk came from brown cows and regular milk came from black and white cowsAnon
- i used to think chocolate milk came from brown cows and normal milk came from white cows Anon
- When I was little I thought cows married horses, cows were all female and horses were all male. — Sheila
- When I was young I believed that the windmills found in farmers fields were used to keep the cows cool.— Linda
- I used to believe that brown cows made chocolate milk and white cows made regular milk.— andrew mient
- I used to believe that brown cows gave chocolate milk, and that white cows gave white milk.— James