Drawing something that is wet and slimy? Here is how to get the look of sunlight bouncing off a wet surface.
This could be an eyeball, slug, or a waxy cap mushroom. You will find this trick can be applied on many subjects. The secret is to overpaint your subject with specks or streaks of bright opaque white. While working in the field, I use Windsor-Newton Permanent White Gauche that I keep in a section of my palette that I reserve for opaque paint.
Click on the first illustration to launch a step-by-step tutorial slideshow.

Once the watercolor was dry, I added permanent white gauche in bold streaks to capture the feel of sunlight through the trees, reflecting on the viscid surface.

With a white gel pen, I added a few last highlights on the caps and the ends of the gills. I love the white jel pen. You get a lot of sparkle for very little work. If your pen stroke feels too harsh, tap it with your finger while it is still wet to blot up some of the white ink. If you do not like the result, the gel pen is water soluble and you can lift it out with a wet brush.