I think this is something to do with a snake is used in the bible, they cheat the first human beings Eve and Adam, that is the reason why everyone who is cheating and being a traitor is called a snake. Actually, with all due respect to the snake, they doesn't deserve it. Snake has the purpose here in our planet. They are one of the animals which balances the ecosystem. They are just killing someone for food and when they need to defend themselves. They are not even named as traitor or cheater, but as a dangerous animals because you could be killed by its venom which is very poisonous. Same goes with people who can put a dirt on your reputation by making stories about you, that is not true. It could be compared to a poison that will kill you inside, instantly.