Internal pipping is when the chick pierces through the egg's membrane and into the air cell, but before it breaks the shell. When it breaks the shell, that's external pipping. Internal pipping is hard to see, because it's inside the egg. You might be able to see it when you candle - it will look like a triangle shadow. You'll know you have internal pipping if you can hear chirping, since the chick needs air to chirp.
