Deck the halls with bowels of holly,
Fa la la la la, la la la la.

The story:

When I was little I had no idea what a bough was and even after I asked my parents about the word's meaning during a rendition of 'rock-a-bye-baby' one night, I had already surmised that the word in deck the halls was bowels and never thought I was wrong.

One night many years ago I went Christmas caroling with some friends and one of them stopped me and asked what I had just sung. I sang the line again for her and she laughed until she cried. To my embarrassment I had been Decking the halls with intestines all these years without even considering the meaning of the word.