@Sokolar
Alice was the princess. She wanted to know the world, but couldn't go outside, so she decided to become a monster that absorbs the memory of the people that live outside to experience things. The humans fought her back and sealed her in that egg. In the previews chapters it was shown that the egg broke, she managed to exit and kill near the rest of humanity.
Also, as others have pointed out, she made a bigger exit hole than him.
EDIT: Lastly, she thinks the snake is her brother as they work similarly, so she freed him by feeding him random people.
EDIT2: Or at least this is my interpretation of it.