On Saturday, I went to Senso-ji Temple in Asakusa to watch a nakizumo ceremony. During the event, babies held by sumo wrestlers face each other in a mock sumo game, two at a time. A referee shouts “Nake, Nake” (“Cry, Cry”) at them and the baby who then cries the loudest is declared the winner. If no baby cries inside of 1 minute, referees will use demon masks to try to scare the babies. The ceremony is religious and has its root in the belief that crying brings good health to the babies and scares evil spirits. It has been going on for 400 years and there are similar events (with different rules) in many places in Japan. I took a few pictures but my zoom is not very powerful. This page has more close-up shots of the event.
Above, opening ceremony.