this might be answered before but I have no clue to what I should look for.
But I am encountering several time that I get "Blacked" faces in Maya and from what I can see I have not interacted with them prior to the change of them.
My question is what is it? and what it the technical reference to it?! I know about set to face but I have not been able to figure out what trick it?!

Thank you in advance.
Any links to information regarding it will be welcoming.