Agar is a gelatin substance refined from certain species of seaweed, red algae to be more specific. It is perfectly edible for humans. In fact, the reason it is often found in health food store is that it makes an excellent substitute for gelatin. Vegans and vegetarians like the idea of using plant based agar over gelatin, because gelatin is refined from animal parts. You truly do not wish to know which parts however, it is nothing you'll find in the meat department of the supper market, trust me. By tweaking the recipie a bit, you should be able to use agar anywhere gelatin is called for. On the other hand, using gelatin in place of agar is not really a good idea. It was at one time done, however there exist many bacteria which can liquefy gelatin. While some bacteria can also liquify agar, these are far less common. One more note of caution, you should never mix eating and agar work. While it is ok to open a new pack of agar to make a jello salad, this should be done quite seperately from mixing agar media. And you should never eat out of a culture dish that has been used for bacteriological experiments.