One thing I’ve noticed a lot about people who sing is they often close their eyes, especially when they get to an “intense” or “passionate” part of a song.
Why do people do this?
You can block out distractions and concentrate on controlling your voice, breathing, duration, transitions and the rest of the stuff.
I do it in an (often failed) attempt not to go flat.
I thought the words were tattooed on the inside of their eyelids…:smack:
The most ‘intense’ and ‘passionate’ parts of a song are very often the most difficult bits to sing. What Hambil said, is basically the reason most singers close their eyes to sing. It’s actually something that’s frequently taught by singing teachers. You want to focus purely on the sound, and it helps shut everything else out.
Although sometimes they’re just doing it for effect, like any body language on stage. Closing your eyes makes you look tense and reflective. It just so happens to be useful in getting your pitch right.
I don’t know about anyone else, but I close my eyes when I sing to enjoy the sound. Like if I’m holding a long note and hit just the right tone. I’m usually smiling at the same time.
Squinting doesn’t help, though, and a lot of people do that.
As a jazz musician, I’d close my eyes to concentrate on the chord changes and what the other musicians were doing around me. And think of what riff I was leading into.
Unless, of course, there was a beautiful blond sitting in the front row eyeballing me! 
It’s a cross of many things. Part conscious effort at producing the desired effect. Part listening intently. Part rapture - of the type that you may have experienced while kissing someone. For a lot of people, making music is one of the true unalloyed joys of life, and they show that joy, sometimes inadvertently, or at least without intentional affect. You make music, sometimes you just swoon - it’s that much fun and it’s (sometimes) that good.
Yeah! I tend to not close my eyes when playing, but I need something to focus on, and it helps to not be staring intently at the guitar player’s fret hand. It doesn’t bother anyone, but it looks weird to the audience, I find. I’ve often thought of carrying a little postcard or cheesecake photo (not too racy) or something to have to look at on the job. I hate looking at my own hands; it’s like a centipede (pace Rebbie! RIP Michael:().
Without something on which to focus visually, I find it’s easy to get distracted from either what’s going on musically or what’s in my own head that I want to execute. Often in conversation I find myself looking away at the sky to people, and it’s kind of offputting, to people I don’t know well. Best to keep it to the stage, IMO.
I do it to block out the looks of horror.
But yeah, it helps me to focus during the more difficult parts of a song.
There are some benefits to looking at the hands while playing that you may not get when singing. I was shedding a few years ago some Don Patterson licks, especially off his ballads, which turned out to be mostly straight diminished scales, and I realized a lot of them looked like strange spider creatures from outer space when visualized on the keyboard.
And no, I wasn’t smoking anything :-
On the other hand some people think that closing your eyes breaks the connection with the audience. I’ve heard this mostly in barbershop style chorus evaluation.