None of the L-Cysteine nodes seem to tell you the most important thing!
Cysteine, or its derivative L-Cysteine, is commonly used in baking; pizza crusts, crisps/potato chips, donuts, Bagels, Croissants, Pita Bread, Crackers, Melba Toast and baby milk formula.
Where do they get cysteine? Human Hair! They grind down human hair, extract it and stick it in your food!
I will say it again because you need to know this... POTATO CHIPS, PIZZA AND BAGELS ARE MADE FROM HUMAN HAIR!
The human hair variety of cysteine is cheap and so is the most common. They get a lot of it from India where tonnes of hair is cut in religious rituals and they also get it from Japanese, Chinese and German heads...
YOU ARE EATING HUMAN HAIR!
It's not kosher either...
You can also get it from chicken feathers and cow horns. It can be produced artificially. But the majority of Cysteine used in USA is from human hair.
Enjoy your meal!