Candle them every once in a while, look for blood rings, toss undeveloped eggs around day 10-14, and also smell them often too, usually you can smell a bad egg before it explodes. I have not had one explode on me yet (knock on wood), But I have several Button Quail eggs in the bator that are too dark to candle, I'm a little worried about that, but I guess it's good they are small, less mess if one does explode.