I used to believe that the expression "The room was literally not big enough to swing a cat" referred to the swinging of an actual live cat by the tail, at arms length, completely around one's body. I have come to understand, with some disapointment, that the "cat" is actually a "cat-o-nine tails" -- a type of whip used for dicipline aboard ships, whose quarters were often insufficient to swing the device with the sought after level of vigor.
A childhood belief about cats and dogs

others believed things like this
- I used to think that if I was swinging on a swing fast enough, I could jump off it and start flying.— Nick
- I used to think that swing music was called that because you listened to it when playing on the swing set.Anon
- I used to think that you would get arrested if you didn't swing your arms when you walked in publicAnon
- that if i swang high enough on the swing set at my grandmothers house...i could catch a cloud for her.— nicole
- --I thought if I swung hard enough in my swing i could possibly reach an airplane
— dusty chenille - We used to think that if you ran swinging your arms around, you would run faster. — Christine