Some time the cycle will get interrupted. They can lay a "soft shell" egg.
Have one with a hard shell with no yellow, have seen one with a hard shell inside a hard shell.
Then of course there is the WOW, double yolk. It may also be noted that if a hen lays an egg very early in the morning and another in the late after noon of the same day, she is apt to miss the next day. This is not to say all early layers will lay two every day.
It is also known young pullets will try to crow like a rooster, so don't mistakenly kill your young pullets thinking they are frying roosters. :'(
There is a lot to be known about chickens, just peck around and you'll be surprised. :) :roll: :)doak