When cooking eggs it may happen sometimes that the egg shell becomes cracked. To avoid this, you can use a little scientific trick. In the rounded bottom of the egg resides an air pocket which is also the one that expands during heating and makes the egg shell break. You need therefore to find a way to let the air escape out of the egg. Simply take a needle or with a very sharp edge point of the knife, make a tiny hole in the bottom of the egg. Then cook it as usual. Note though that this not always works!