Why doesn't the smudge tool work? – Caricature - the digital drawing app for people who love to draw. Free. Lite. Review

Smudge tool is grayed out. Why? Is this something I have to purchase? Why do I have to add numbers before I'm allowed to use this app. It's annoying.
Review by GC in USA on Caricature - the digital drawing app for people who love to draw. Free. Lite..