Tar is a black, viscous substance made from different types of carbon.
Kevin McCallister coated the basement stairs in his home with tar and let it set for some time. He intended the tar to inconvenience anyone walking on them by forcing them to remove one piece of their footwear with each step.
To further the discomfort, Kevin used the tar to glue a nail in place. Marv Murchins walked through the tar and soon ended up with tar-covered bare feet. He then stepped on the nail protruding upward and screamed while falling backwards onto the floor below.