We all know the Old Testament story of the Bible where Satan came disguised a serpent and tempted Eve to eat the fruit of knowledge. The eating of the fruit of knowledge was an open vista into the domain of sexuality. It’s said that after eating the fruit Eve and Adam became ashamed of their nudity and covered their loins with fig leaves.
Ask the Serpent as an idiom means asking a person out for sex.
Example: I said to my mistress: can I ask the Serpent?