scooby doo and the spooky island body possession - YouTube
When Dante describes the spirits in hell as "shadows" this is how I imagined them. Even though each circle of hell is different and people have varied forms of their human body, I would say this is a pretty close representation of the shadows. As Dante goes further into hell, the spirits have a more body like figure and can be touched or held like Shaggy is holding Velma. The spirits in the well that shaggy is looking into are like the spirits constantly chasing the banner that can never be reached. Like the runners, these swirling spirits are tortured by the desire to return to their bodies.