Pipping is where the chick pecks a hole in the shell. Zipping is where it continues to peck from that point around the shell until it is divided in half. Then it pushes the halves of the shell apart with its head and its feet and hatches. The gunk described sounds like the allantois, which is a storage sack for the little bit of waste the chick produces in the egg (similar to meconium in human babies which is retained in the intestine but can be released before birth). It is left behind in the shell when the chick hatches. The kicking around before hatching may have torn it open so its contents leaked out.What does zipping mean? I have never hatched any chicks.