According to their special penguin bog: "When the chick reaches its hatch date it will use its beak and break through a membrane inside the shell into the air space

"The chick will then start to break the shell from the inside out. From the outside the pip will look like a tiny raised spot or a crack on the egg and as the chick continues to pip a bigger and bigger hole can be seen. You can sometimes see the chick's beak poking in and out of the shell and hear the chick peeping from the inside. The whole pipping process can take 24 to 48 hours before the chick is free from its shell."

Watch the video below to see for yourself: