Chews are made from cattle or horse hides, their journey starts with the hides sometimes being soaked in a toxic sodium sulphide to remove the hair/fat.
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Chemicals can be used in order to split the hide into layers, they are often washed with hydrogen peroxide to give the white pure look and remove the rancid smell.
Some chews have shown traces of arsenic, mercury, chromium and formaldehyde. They have been known to cause intestinal blockages, and there have been reported cases of poisoning from chemical residue and choking. The chews go slippery when wet and cause choking.