Couple posts ago I mentioned using practical elements in the From Inside animation. Here is a simple example (that also happens to be one of my favorite shots).
In case you've never heard the term before, "practical" in the sense I am using it simply means "real stuff." Practical special effects are effects that are done on-set without computer generated tricks. Examples: fire, smoke, explosions, rain, gunfire.
One of my favorite uses for practical elements is to blend them with computer generated animation. (The waterfalls of Naboo are salt...)
This is how the shot started. Dripping white latex paint in front of a black background.
Next, I push the contrast & brightness of the white paint until it becomes very high contrast. This high contrast shot is used as a mask for whatever color I want to make the drips.
The drips are then attached to an animated oar. In this case, about 4 separate drips. Each one is motion-tracked to follow a point on the moving oar. Final shot:
That's it. Simple, but effective.
Back in a few days w/ another example.