When you leave grains in your mouth for long enough, they'll turn into flowers of bacteria. These aren't the nice, pretty flowers you'd give your mom on Mother's Day. These are little bacteria flowers that are taking over your mouth. Maybe brush your teeth next time.
There is a lot of this bacteria in the King (きん) of England's mouth. He eats a lot of grains, and he won't let anyone touch his mouth to clean it, but he refuses to do things himself... so it's absolutely chock full of bacteria.