I used to believe that if you held guinea pigs up by their tails their eyes would drop out. I couldn't test this as I could never find their tails.
A childhood belief about general

others believed things like this
- I used to believe that if you held a Guinea pig upside down, it's eyes would fall out.— james
- That hot dogs were made from rat tails.Anon
- When i was little, i thought dogs poop from their tails.Anon
- When I was little, I used to believe that wind was caused by whales flapping their tails way out in the ocean.— Nanohawk
- I used to believe that waves were made by whales who lined up in a row and flapped their tails.— Passionola
- I thought a Monkey was just a baby Gorilla and when they grew up their Tails fell off!— Brainhead