Liquify

I'm trying to use liquify to make a small change in facial expression in the icon in this picture, but nothing is happening! I can't figure it out. I've used liquify once before and it worked fine, and nothing I googled or found in the memories helped. An screenshot with all the irrelevant stuff cut out is below the cut; that's the icon I'm working on on the left. I want the left side of his mouth to curve up more so he's smiling more. Is there anyway other than liquify to do this? Also, I use Photoshop CS2.