O air-filled cavities that secrete mucus to keep the nose moist and remove bacteria.
The least reliable source of safety information is celebrity athelte
"When water molecules escape from your frozen food, it is also possible for oxygen molecules to seep in. The oxygen molecules can dull the color and modify the flavor of your frozen product. Food that has freezer burn is safe to eat, but you may find the texture and taste not to your liking."
Source - https://www.loc.gov/rr/scitech/mysteries/freezerburn.html
