I had watched an episode of some show, I think it was The Wonder Years, where they had to get a dog "fixed". Of course, being a family program they didn't say what "fixed" meant, and I didn't know what it was, except that on the show the dog kept barking all night before they got him "fixed" and then afterward he didn't. So, at my tender age, I thought that getting your dog "fixed" meant that the vet would make it so the dog couldn't bark any more by taking out its vocal chords or something. I believed this for a couple years, too.
A childhood belief about cats and dogs

others believed things like this
- I used to think that 'black comedy' was show like Family Matters and The Cosby Show.— Katie
- I thought that socialism just meant being social and didn't get why anyone would be against it!— Olcasgean
- Up until I was 17 I thought that 'no outlet' signs meant that the steet didn't have any streetlights.— Kelsey
- I thought when someone was described as being "mild-mannered" it meant they didn't have very good manners— Samilton Duerheiser
- As a kid, I thought "No Outlet" signs meant the houses past that point didn't have any electrical outlets.— Julie
- I fully believed, up until about 6 years old, that the word 'accident' was a noun that meant 'burnt toast'.— Karl Goetz