system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Reptiles are air breathing animals. However, when they're in an egg, they have no source of air like mammals do in the womb. How do they survive without air while developing?
gpt
When the egg is laid, it is very warm, as it cools, a thin membrane shrinks away from the interior, creating a pocket of air. The developing animal uses this air, and exhales CO2, which is pushed through millions of pores on the shell, allowing fresh air to come in. 


This is similar for both lizards and birds.