By putting a negative value in for time we can get a layer to trace out a portion of the path that occurs before time zero. Whatever time you specify, you get the wiggle() value that would occur at that time. This parameter works very much like the valueAtTime() method you can use to retrieve a property's value at any given time. We are able to access these negative time values of wiggle() by using the seldom-used fifth parameter of wiggle() - time.

The blue dot is tracing out the portion that occurs between zero and positive three seconds. The red dot is tracing out the portion of the path that occurs between minus three seconds and zero. The trick is that the red dot is tracing out the three-second portion of the path that occurs before time zero. It turns out that the red and blue dots are actually tracing out the same random wiggle path. That seems like quite a coincidence, right? Well, there's a little trickery going on here that is key to making this all work. Notice that it starts near the right edge but ends up in the lower left corner - exactly where the blue dot starts. Now examine the path traced out by the red dot. It starts in the lower left corner and ends up near the middle of the right edge after three seconds. If you examine the lower movie to the right you'll see such a path traced out by the blue dot. Visualize a graph showing the path that our layer traces out as it moves randomly from time zero through three seconds. Let's say we want to create a three-second loop of wiggle motion.

Easing wiggle expression after effects