Maybe cute snake videos ?? And explain to him that they are very docile and sweet. My mother is a very religious person, when I convinced her I told her no one can control what they are and what they look like before they are born, so why judge based on appearance? That argument worked well haha.
But please remember to respect your parent's wishes, no means no. Don't bug them about a snake if they say their final answer is no. If its a no, remember that you can always get one when you move out.