a scientist carefully places a fresh sandwich into a clear glass container with a thick rubber seal around the lid. She presses down firmly on the lid until it clicks into place with a satisfying snap. The rubber gasket compresses tightly against the glass, creating a perfect seal with no gaps visible. Her assistant watches as she tests the seal by gently trying to lift the lid, but it won't budge. The vacuum-sealed container sits perfectly sealed with the sandwich preserved inside, showing no air can enter or escape. something that is completely sealed and not allowing air to get in or out