Special Effects - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 261

Figure 4.59
3. Use the Zoom tool (Z) to zoom in on the area you wish to liquify.
4. I want the area around the fighter's eyebrow to be swollen, but I need to ensure
that other areas aren't affected. I use the Freeze Mask tool for this ( Figure 4.60 ).
Make sure the Show Mask checkbox is selected ( Figure 4.61 ), and paint over the
areas you want to protect. In Figure 4.62 I've painted an area in the middle of the
fighter's eye.