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Next Duplicate human layer.
Select this copy and choose Adjustments->Gradient Map (makes it black & white).
Go to Filter->Blur->Surface Blur. Adjust so skin is smooth.
Hit Command-L to adjust so darker shadows appear but allowing highlights.
Save this black and white copy as a PSD.
Now hide or delete the black and white copy.
Select the tiger layer and make the opacity about 50%.
Drag it over the human face.
Go to Edit->Transform->Warp to fit the tiger face over the human face.
Most importantly, try to line up the eyes and the nose.
Hit Enter to accept.
Select the tiger. Go to Filter->Distort->Displace.
Adjust vertical and horizontal scale to both 5 (or as desired) and chose Stretch to Fit and Wrap Around. Hit Ok.
Browse to the black and white copy PSD and hit open (this will use the contours of the face to make it look more realistic). You can now set the opacity back to 100% on the tiger layer.
Next select the tiger thumbnail and set the blend mode to Linear Burn.
Next, go back to the layer mask on the tiger and brush more precise adjustments down the center of face and around the eyes. The human eyes should be showing through. Leave some shadows in the eyes so it gives it a little realism.
Remember black takes away the layer, white adds back.
Next add a new Hue/Saturation adjustment layer.
Adjust the Saturation to about -65.
Select the layer mask on the adjustment layer and using the brush(black) paint over the right side of the face so the colors of the girl come back to normal.
Next merge all layers (or go to image duplicate to save a backup).
Go to Filter->Liquify. Pull some strokes across the fur to the forehead. Add any other small strokes down the center of the face as desired.