To show respect for their lord
Bowing your head is a sign of respect. Closing your eyes is to concentrate on your prayer.
They also kneel,stand, Face the east, Rock,ect,ect. It all depends on what Club/Religion they belong to. Don't forget the secret handshake. :)
To show respect.
That is respect to God and also to shut out the things around an concentrate but one doe snot have to close their eyes to pray,Jesus looked up at heaven and prayed to his Father.
And sometimes, when they're through with their prayer, they look up to the sky and raise one hand with an extended finger. I guess that signifies something too but, I don't know what.
Maybe to ignore the evidence of it's ineffectiveness?
It's a show of reverence, that we're humbling ourselves to who we pray to. At least, that's why I do it.