Really nice interview by Simon Carter with Aussie Chris Webb Parsons:
Oh, my thumb. I use it like another finger. When I first started climbing I was reading about how to get stronger, about finger boarding etc. I figured out that there was a lot of strength in my thumb and I remember sitting in school, my maths class, and I was just mucking around on the edge of the desk and I was playing with my fingers and I had my thumbs on the edge of the desk and I was like I wonder if you could use that as a crimp? So I began twisting my thumb and really stretching them, every day, stretching them. I remember they were really hurting. But I just kept crimping the edge of the desk and began to use it on certain holds.