Most unusual, I think, are the twisted silk perles. Here are photos of two of these rocks:
Here's the silk perle (metal core with wound around it) thread you start with the make the composite threads and a photo of several of the completed composite threads. To create the composite threads, you run a strand of filament silk through the center of the silk perle, then stretch the silk perle out until it's getting close to straight. Repeat the process with a different perle and color of filament silk. Then twist those two threads together. . . and the result is the threads shown in the lower photo. The interesting thing about making these threads was how hard it was (for me at least) to predict the actual look of the new thread from the colors I started with.
To round out the grotto, there are also two rocks made of French knots of Silk Perlee. What an assortment of threads in a small area!