Wave 2d effect : help required

Hi,
Have a look at this flash intro http://www.delamelon.com/flash/body%20blows.swf

I'm trying to get an effect like the purple 'wave' at the bottom of the screen but can't think of how to do it. Any ideas? Do I create a line an move it by the opposite of each line's ends coords? Any tips appreciated.

Thanks.

It looks like a large rotating rectangle to me.

Yeah just set the handle position offset to the top middle of the rectangle and rotate it back and forth

Graphics 640,480

SetColor(180,160,160)
DrawRect(0,0,640,320)

Local img:TImage = CreateImage(640,320)
GrabImage(img,0,0)
SetImageHandle(img,320,0)

Local angle:Int

SetClsColor(48,96,64)

While Not KeyHit(KEY_ESCAPE)
	Cls
	SetScale(2.0,1.0)
	SetRotation(Sin(angle)*15)
	DrawImage(img,320,240)
	Flip
	angle :+ 1
Wend
End

Thanks everyone especially zawran for the code. Now it's time to sit down and understand whats happening and be able to replicate it myself.

Many thanks.