I thought the story he was telling was legitimate, then he added some random useless information to make the story seem more believable, then I knew he was faking the snake.
To add a seemingly random and/or useless detail to a story in order to make it more believable.
"So, one time when I was working as the cashier, this massive guy came into the store, wearing this odd shirt of a cobra..."
"Alan, are you faking the snake with me?"
Metaphor. Similie. The snake is one or several fingers (can include another person's help, toys, etc.). Your fingers explore and slither around your body, finding places to penetrate or just brush past. Let the Snake so it's thing. Pretty soon you'll have an orgasm.