https://www.cbc.ca/kidscbc2/the-feed/why-do-some-people-have-outies-and-some-have-innies
https://www.nbcnews.com/healthmain/what-makes-innie-innie-more-belly-button-mysteries-1C6437359
https://www.mentalfloss.com/article/557098/facts-about-belly-buttons
https://wonderopolis.org/wonder/are-you-an-innie-or-an-outie#:~:text=Most%20people%20end%20up%20with,known%20as%20an%20umbilical%20her