There has got to be some reasoning for eggs not being incubated. It sounds like you have a lot of info and should start logging it down. Do you think you that your girls planned on eating those eggs that she was not going to incubate. Or do you think she planned on just letting it go with ambient temp/ taking turns with It etc. Maybe population control? DO you have enough info to make a hypothesis? This is good stuff, this is what I was looking for. Are the snakes that hatched out of the stray eggs healthy? healthy as hatchlings, etc.? In regards to the heartbeat thing If a ballpython can sense temperature differentiations of 1/200th degree I think they can sense a fertile embryo after it leaves its body for more air. Let me know what you think.