Go get a fresh boneless skinless chicken breast. Put it inside a Zip-Loc bag, so that a few inches of it is still hanging out. Put it on a plate, in the fridge. Leave it overnight. Take it out, now, and look at it. Notice the way that the uncovered meat has become considerably darker than the covered.
That is how my tongue looks.

Go get a mirror, a tissue, and a tube of red lipstick. Dry your tongue with the tissue. Dab lipstick on one corner of your tongue. Moisten your tongue, without wiping off the lipstick.
That is how my tongue looks.

That is how my tongue looks.

My tongue was normal yesterday. (Actually, it's always been a tad bit long.) Now, a portion of my tongue no longer has a wet look to it. It's darker than the rest of my tongue.

I [stupidly] licked a knife yesterday. It just barely scathed the surface of my tongue. It didn't bleed, it didn't pus over. It was just a simple linear papercut-like slice. So why the hell is there a DARK DOT on my tongue?!

Fuck off, Dot.