Back in 1971 two girls I knew did this. They sprinkled some weed into the Christmas Day pasta sauce. At some point late in the meal they suddenly realized that the entire table (grandma included) were hysterical with laughing. They got kinda scared at that point but nothing worse happened.
That happened at my office. We were billing out a big project with very detailed packing lists. The typist was typing like mad and it was just gibberish coming out.