How does Sasori make puppets?

He drains their fluids and all the stuff inside them first (after killing them), then I think he adds wood I know the process probably isn't pretty...I like to call it "Puppetatized." These series of events are in the art of Kugutsu. Sasori owned 100 puppets, which he used against his grandmother, Chiyo, to capture the new Kazekage, Gaara to fulfill Akatsuki's plan to have all the tailed demons. Sasori was killed by this battle.