Why does the egg hatch independently to go looking for hosts?
It’s true that usually, the eggs lay dormant until a suitable host approaches them, they tend not to go looking for victims on their own. This egg is different in that not only do the larvae (aka “facehuggers”) hatch on their own but it carries at least two larvae. One of them is seen in the beginning of the film stretching its fingers but is then presumably killed when it cuts itself with Newt’s cryotube glass (which explains why Newt was not infected.) Another one manages to break through Ripley’s cryotube and successfully facehugs her. Then, on the surface of Fury 161, we see yet another facehugger that goes on to infect an ox (or a dog, if you watch the theatrical cut, but I highly recommend the director’s cut!) This tends to give credence to the “emergency egg” theory.
