So it needs to be a circle itself and not a circular shaped object. Gotcha.

[He lapses into silence, studying the chalk circle on his floor and the empty bottle inside it, trying to let go of his sense of logic just enough to see if this would work.

Though he was friends with a Jedi, he was still a skeptic at heart. He tended not to believe something unless he saw something.]

So I just prick a finger and drop a little blood on the circle? What's it supposed to do? Like...how does it work?