Step 1:
To start off, create a new document 500x500px with a white background.
Step 2:
Select a soft rounded brush with a diameter of 45px. Set both the opacity and the flow to 35%.

Step 3:
Next, set the foreground colour to #660000.
Step 4:
Using the brush tool scribble on your white canvas until it looks like something in the picture below.

Step 5:
Set the foreground colour to #990000 and scribble some more onto your canvas.
Step 6:
Set your foreground colour to #CC0000 and keep on scribbling on the canvas. You should now have something that looks like this.

Step 7:
Now select 'Filter' then 'Artistic' and then 'Plastic wrap'.

Step 8:
Set the 'Highlight Strength' to 5, and 'Detail' to 15 and 'Smoothness' to 5.
Step 9:
After you have applied them settings, click on 'Image' then 'Adjustments' then 'Brightness/Contrast' and set the 'Brightness' to -25 and the 'Contrast' to +40.

Step 10:
If you have followed all the steps in this tutorial correctly you should have something that looks like this.

Another variation can be found below.

Step 11:
I hope that you enjoyed learning how to make guts in Photoshop and will try different methods to create different variations.

