He had the voice of a man ,or people in the garden of Paradise. He could speak even Adam's own language. And he understood the language of God. So, therefore, it was not a real snake, as someone has made you to believe in the past to blind you further to the knowledge of actually who the serpent really is. They said that, even, the snake used to walk, but having the language to speak and converse with human beings was also to be reckoned with.
Alligators go on four feet.
There are other reptiles, today, that are crawling and walking on four feet and swimming in water, but they don't deceive us. They are not smart enough. Nature didn't give them that intelligent brain to equal our intelligent brains. This particular dragon is the head of the nation or race. And therefore it is mentioned clear enough for you and I to understand, here in the third verse, that he had seven heads and ten horns and seven crowns upon his heads.