What poems suggest that dogs can't change shit?

Dogs eat arrows, and their sex is also. The rivers and mountains may change, but not one's essential nature

Dogs eat arrows, which naturally implies that dogs can't change the truth of eating shit. In ancient times, it was observed that dogs would eat some rotten meat and bones and even feces when they were in the wild. They think this is the nature of dogs, because dogs are carnivores and omnivorous, so they will eat something that is not conducive to human consumption. This sentence means that the dog's nature determines that it will eat shit, just as it will eat other foods that are not conducive to human beings. Therefore, people think that dogs can't change eating shit, because it is their nature.

The rivers and mountains may change, but not one's essential nature Jiangshan here refers to people's external environment and conditions, and temperament refers to people's internal character and habits. This sentence means that although people's external environment and conditions can be changed, their internal personality and habits are hard to change. The meaning of this sentence is that dogs' behavior habits are as hard to change as people's personality. Therefore, people think that the dog's nature determines that it has to eat shit.