If you're using water, then add some food coloring. Just make sure the hand doesn't get visually lost in the color of the punch--you want to use contrasting colors.
[header] How to make the arm of death [title] Pour some water or orange juice into a food-grade rubber glove. [step] Leave enough room at the top for tying a knot and for adding gummy worms. [substeps] Since this has the potential to be slightly messy, pour the liquid over a sink to take care of any spills.