Your body needs oxygen to function — and that was true even before you were born. As you grew inside your mother's womb, even before you had working lungs, your cells were crying out for oxygen. And your mother kindly answered that call. Oxygen and nutrients from her blood made their way down your umbilical cord, through your belly button, and fueled your body.
Now consider a chick — before it has hatched. It's cut off from its mother by a hard shell and a couple membranes. There's no way for the hen to get her still-developing offspring the oxygen it desperately needs; the pre-hatchling is on its own.
So why don't bird embryos suffocate inside their eggs?
In Skunk Bear's newest episode, we use the magic of animation to take you inside an egg and explore the delicate system that keeps these little things alive.