I remember a case from decades ago in which a child wandered into a neighbors yard and was killed by a tethered wolf hybrid. The mother of the child sued the animals owner and the breeder of the animal. So I think he should sue everyone involved in putting that python in that owners hands-the breeder, and whoever they got the snake from, if different. They should also sue the tank manufacturer, and manufacturer of the blanket that covered the tank, for aiding and abetting.