Liquid nitrogen looks like boiling water that produces fog, given that the nitrogen of the surface evaporates really fast.
One teacher used to sacrifice mice by immersing them in liquid nitrogen while holding them by their tails. Nasty. The poor mice died instantly, so the teacher argued this was a humane way of killing them. Still, the contorted "mousicles" he pulled out of the liquid nitrogen container still give me nightmares.
I think about this a lot when I think of IVF and frozen embryos. I've talked about embryos before and stated that I don't really think of them as children. But I do know they are alive, and the idea of immersing them in liquid nitrogen gives me pause. I've frozen cells many times, mostly mouse cells and a few HELA cells and a bunch of different bacterial cells. Most of the time I was able to bring those back to life, and I'm sure the same applies to frozen embryos. And yet, there were a few occasions when a strain or a cell line was lost during thawing, without there being any reason. The cells just failed to come back to life.
The loss recently suffered by amiracle4us, who was hoping for a FET, reminds me of the fragility of "sound science". Very often, science fails us.
Could I take such a loss if it came to my embryos? I think not, and my prayers go out for those who have undergone such pain.