First off, I believe you need to isolate your actor on one layer. Shooting in front of a greenscreen would be best, but you could also do this using masks and a lot of painstaking work. Actually, now that I think about it, for a displacement effect you could film him in front of any evenly colored background, and it would work ok, but a keyed out or masked out actor will work best. Then place this layer over the top of your background plate.
Then you set the Composite mode (in the timeline) on the layer with your predator to Displacement. Use the sliders in the displacement controls to adjust the subtlety of the effect to your liking.
I think that's it.
NOTE: Even with a solid background still behind the actor in the shot, you can still get the desired effect with displacement. However, the very edges of the frame might get ugly lines in them as a result. If you use properly keyed footage of your actor, you will not have this problem. Displacement works on color info, so any variation in colors in the background of your displaced layer will cause displacement ripples in the final shot.
Last edited Thu, 11th May 2006, 11:17pm; edited 1 times in total.