Smile! It helps your brain think.
Did you know that your brain tends to look for the easiest answer, especially if it's under stress? Since that easiest answer probably isn't the most correct one, you can help it by smiling.
Research* shows that when you frown your brain thinks you're hard at work thinking about something difficult. It doesn't enjoy these states of cognitive dissonance and strain, and the frown is reinforcing the idea that oooooh, this is hard.
Next time you're trying to crack a really hard puzzle, smile. Send good, hey this is easy! vibes to the brain, and let it help you naturally come up with more (and hopefully correct) options.
Image by Takashi Hososhima, Flickr, Creative Commons License