"The cooled, bubbled-up effect on some areas of the blasted tunnel walls was created by first using inflated balloons pinned to the tunnel walls. In film tests they looked like balloons stuck to the walls, so the effects crew tried smaller inflated latex condoms. Further testing showed these looked much more convincing, and the crew wound up inflating more than 3,000 and then sticking them to portions of the tunnel set's walls." #monsterdon