If you hold clothes in place when they’re still wet, they’ll freeze
Anything that gets wet when the temperature is under 0°F can and will freeze. Even your clothes can become rigid if they’re humid. While this may be a tragedy if you get caught in a snowstorm, some people take advantage of it to play pranks on others and scare them.
According to the Internet user that shared this photo, people at their university take children’s clothes, dip them in cold water, and hold them still until they freeze to fill the campus with “invisible children.” We feel sorry for the security staff at their university, though. They probably got a few tiny heart attacks from seeing these things.