Onion has yellow center. Is it safe to eat

I think it would depend on the cheese.

• For a reasonably hard cheese, like cheddar, I have done it, and never gotten sick (your results may vary).
• If it's pre-grated, then I would not touch it anymore.
• For a softer cheese, like a brie, I would not risk it.

-- Hair is a protein mostly keratin

Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails.

There's nothing special about it as a protein, so as long as it doesn't wrap around your tonsils and get stuck in your throat, or contain dyes, hairspray etc. it's safe to eat. However, the long stringy nature of the stuff can cause problems if you eat too much of it.