Roy has painted a big story from northern Spinifex country called Pukara.
Pukara is the story of the Wati Kutjara or "Two men" who are travelling through the country on initiaton business. The snakes represent a father and a son.
The Kalaya Tjukurpa (Emu story) are also present at this site and you can see this by the many emu tracks in the painting.