What is a heifer cow? A heifer is a mature female cow that has not calved, or given birth to a calf, yet. As soon as a heifer gives birth, she becomes a cow. A cow refers to a female of any age that has given birth.
When most people think about gas masks or respirators, what they usually envision is a tight-fitting plastic or rubber face mask with some sort of filter cartridge. The mask covers the nose and mouth. These are called half-mask air-purifying respirators.
Masks can shield us from danger or can suggest danger to others. They can be part of our assumption of what we would like to be, or of what we fear we may become. We can laugh at the mask, or run screaming from it. And the mask can transform its wearer so as to assume the character of a very different person or of a being from some other world.