Sadness

Well, I doubt that this bird is as sad as it looks, but it's still a cute photo. I remember how I used to draw smileys back when I was a kid, and how eyebrows were able to determine smiley's behavior. If you put his eyebrows like this / \, you get a sad smiley (if his mouth are doing sad face), and smiley that just pooped your carpet (if his mouth are doing happy face).

Then again, if you used \ / for eyebrows, you get a proper pissed off smiley if you draw a sad mouth face, and mean smiling smiley if he has a happy mouth face. Compared to former case, this is a smiley that pooped your carpet, but then took part of what he did and stick it to some other smiley that will take all the blame.

That being said, here's a bird that doesn't have eyebrows, but in all the other ways depict what I'm talking about - sad faces, happy faces... Of course, my point actually is about his eyes that are eyebrows-less, but look as if they have some...

definitely a / \ eyebrows.

And here is another example... Take a look at the cat on the right... 

this, my friends, is a great case of \ / eyebrows.

All the images were found on imgur.