I'm not a fan of re-freezing uneaten prey. If it's been laying around (fully thawed) for very long, that allows way too much spoilage. If re-frozen promptly, the main thing you'll lose is "quality"- ie. when re-thawed, it's likely to be mushy & fall apart easily- but if it was thawed for a longer amount of time, it's likely to be spoiled & most snakes won't accept it anyway. Remember that freezing doesn't kill bacteria- just puts it on hold, not growing until temperatures are once again favorable. Bleah...