Most of the time, people don't take a lot of joy out of a baby crying. This festival's the exception.
In the Nakizumo Festival, held throughout Japan, sumo wrestlers hold babies and make weird noises and faces in an attempt to make infants cry. The baby who cries first (or, if two babies start crying at the same time, the one who cries the loudest) is the victor.
The tradition is hundreds of years old, with mythical roots. The Japanese have a saying, "Naku ko wa sodatsu" ("Crying babies grow fast"). It was believed that a loud cry from an innocent baby will scare away demons, ensuring that the kid grows up healthy.
The festival has a silly, festive air to it, so many of the babies don't cry. Fortunately, or perhaps unfortunately, sumos sometimes will put on scary masks to goad them into it and shout "Naki! Naki! Naki!" - literally, "Cry! Cry! Cry!"