When 7-year-old Jimmy Striler dons his Red Ninja costume this year, he will be armed with a plastic sword. He will also carry something else St. Louis, Mo., children must have with them on Halloween: corny jokes.

In certain haunts, such as this city and Des Moines, Iowa, the end of October isn’t just an occasion for children to dress up like a ninja, a ghost or the latest Disney cartoon. It is also a challenge: Make an adult giggle. These Midwesterners don’t parcel out candy free. Trick-or-treaters have to earn it.

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