One of Life's Great Mysteries

Pardon me while I delve into something that might seem socially uncouth...

I understand why little boys and little girls pick their noses. I get it. Heck, I do it myself from time to time, much to my Beloved's consternation. But what in the heavens and earth possesses that little boy or little girl to take whatever they find inside the recesses of their nasal cavity and then put it in their mouth?!?