I want to add something to this:

Time and again, I see people say 'There's something wrong with my pet, but I cannot afford a vet right now'. Their solution is to do nothing.

That lack of action is not ethical, moral, or legal. Taking a sick or injured pet to the vet isn't optional. It's required by law. If you cannot afford it, then what you need to do is surrender your pet to a rescue or shelter that CAN get it medical treatment. Selfishly keeping it until it dies doesn't show any sort of love or regard.

Many people don't seem to understand that if you can't afford the vet--you can't afford the pet.