I did this on a friend of mine.
We each had to write a story and read it to the class.
One guy, who although he was very popular, had horrible stage freight and I knew from previous episodes that he would hold the paper up to his nose and read word for word.
His story was about a family trip to a relative in Boston and in it he also mentioned that they toured the USS Constellation.
I secretly changed the USS Constellation to the USS Constipation to see if he would read it anyway.
He only realised afterwards what he said but he did get a kick out of it.
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What is stage freight?