After having had a positive experience with slitting, I think that I will keep doing it. It takes a steady hand and like Thomas said, you cannot cut that sac. I like slitting because I have heard of babies that were on the small side, dying because they were stuck in the egg; they were fully formed but could not pip through. I think that for me personally, this outweighs the possibility of killing them by slitting. It is really hard to describe how to slit if you are not here watching, so I would leave that to someone else. I would no slit before day 60 with eggs being incubated at 88 degrees.