For a project I'm currently working on, I needed to draw a mouse with a tumor. In doing this, I came across a neat trick for depicting fur. In Photoshop, you just go to the Filter menu and choose Noise -> Add noise, and go to about 10%. Then, add a motion blur from the same Filter menu. It's not the most realistic but I think it's not bad for a mouse that is just a part of a larger illustration and partially obscured by a Kaplan-Meier plot.