Poor as a dog is also an Internet term, which actually comes from a previous popular saying "as tired as a dog". The term "poor as a dog" is mostly a mocking simile. Dogs do not know how to use money, so there is no such thing as rich or poor. However, using a dog as a metaphor essentially means having nothing.

In the past, people would say that they were too poor to raise the pot. Times have changed, and the reference that can be used has also changed. The more modern poor-adult dog came out. Anyway, there is no money to spend.