Chickens have a good chance of pecking metal when pecking. Many of them are heavy metals. After these metals enter the chicken, most of them gather in the chicken's head. Heavy metals are toxic to human body. So try to eat less. It is ok to eat once for a long time, and don't eat too much.

Ducks eat more water, so they have little chance to contact with heavy metals. It doesn't matter if they eat more duck heads.