Scientists have been researching eye of newt (seen via Next Big Future):
Eight years ago, he and his wife Katia Del Rio-Tsonis, a biologist at Miami University, succeeded in causing tissue to regenerate where it never had before. In a newt's eye, the upper iris can regenerate a lens after injury, but the lower iris cannot. By adding the right mix of certain growth factors – sort of like a recipe – they were finally able to induce the lower iris to grow a new lens. Nature published the findings in 2005.
I'm sure toe of frog is next.