Oakum
Oakum can be used to seal cast iron pipe drains. After setting the pipes together, workers pack oakum into the joints, then pour molten lead into the joint to create a permanent seal. The oakum swells and seals the joint, the "tar" in the oakum prevents rot, and the lead keeps the joint physically tight.
Today, modern methods, such as rubber seals (for example, gaskets or o-rings) are more common.
Saltine cracker
Flat saltine crackers have perforations on their surfaces. During baking, the outer layer of dough hardens first, restricting out-gassing of evolved gasses. The perforations connect the top surface to the bottom surface to prevent the cracker from pillowing as a result of these evolved gasses.