I'm no doctor, but blood in the stool sounds serious. Tell him to go to the doctor!

There is a condition called Black Furry Tongue, it's where a fungus grows on your tongue overnight, all you have to do is brush your tongue well.

I used to get it in High School, I'd wake up with an old cheese taste in my mouth and kind of gagging, it just happens when the conditions are right in your mouth for that fungus to grow.

It's completely harmless.