How do female sheep (ewes) show aggression (biting, head-ing, etc.)??r=1249407866?

I don't think 'aggression' is the proper word. Dominance would be a better term and typically sheep use their heads to into sheep they don't like that are of lower status (although rarely head to head - that's more often seen in rams). They don't bite each other. They can warn each other away by raising one of their front legs without the knee being bent - a rather stiff legged wave . That's a threat display. Keep in mind that the heads of sheep are very well reinforced and they can deliver a lot of power with a head blow. And they tend to be very intolerant of young/less dominant sheep and will hit them repeatedly until those sheep move off.