Step 1: Add Zipper & Select Raw Face Area
Once that's done, make sure you have a duplicate layer of the normal face. Then go to that duplicate layer, grab the pen tool and select the skin of the face enclosed under the zipper. I decided to do this part of the face separate from the neck - as the effect looked better that way. You can do it either way as you need to take the same steps to achieve the effects on both parts of the face. Once selected all the way around, then Right click, Make Selection (2 px Feather). There are a couple ways of doing the next step. To make things easier, we will then go to Edit, Copy. Then File, New - then hit PASTE to paste in this chunk of the face. Duplicate the layer.
Step 2: Bloody Face Insert - with Curves & Colors
Change the meat layer settings in the Layers area - see graphic to know the settings I used. This is up to you - plus or minus in the opacity and fill area. Then on the Layers pallet, right click on the chunk of skin layer, hit Select Pixels. Then go to Layer, New Adjustment Layer & Color Balance. Change settings like the image below or adjust according to how you like it - you can easily change it more later.
Right afterwards, click back onto the chunk of skin layer and be sure the pixels are selected, then go back to Layer, New Adjustment Layer, Curves. Check the Layers pallet and move this layer above the Color Balance layer and above the skin chunk layer - so it will be Curves layer, Color Balance layer and Skin chunk layer. Then go back to the curves layer and adjust accordingly. If you move it certain ways it will make the skin look more raw, a bit glossier with almost the look of fatty chunks to it. It's disgusting - but works!
If you noticed, my image is showing me working on this already on my main image but I recommended that you work on a separate layer to create this. One done, you could flatten your graphic and select it, Copy it and return to your main image. Your main image will already have that area you selected earlier, selected - so then go to EDIT, PASTE SPECIAL, Paste into and it will go right into place!
Step 3: Creating a Larger Cheek and Flap of Skin
Take the Pen Tool out again, and make points around the cheek where you want to extend it out. See image as to how I did it. Then once you go around to the starting point, you'll need to MAKE SELECTION and feather it 2 px. Then go to EDIT, TRANSFORM, WARP. Move the points around, pull them as needed to get that cheek curved properly without distorting it too much! If you have any issues with objects near it looking odd, like my hair problem. Please refer to graphics below on how to easily blend and fix those up.
Also, if you want your red face below to be pulled and distorted to fill in some of that space more, just do the exact same technique on that layer.
Step 4: Finishing Touches
I took a soft brush with a very low opacity and 0 level of hardness, then sampled the color of the cheek where I wanted to highlight, then changed that color to make it slightly brighter - then used the brush to make some highlights on parts of the cheek. I did this to make it look more real and a little shinier in spots.
I used a "scar" brush to make the skin near the top of the zipper look a little indented. The brush was downloaded online - then I made the color of it the skin color and messed around with the effects - adding a little bevel to make it look like it does.
The scab on the cheek was also created with a brush!
If you have any questions please let me know. I tried to make a video tutorial but my software wasn't working so I tried to make these graphics as detailed as possible! Good luck!!!