Bite a tree's root with your fang to get an approximation on its age. It won't be exact, this isn't scientific or anything, but it will be pretty close.
As you're recording your approximation down, somebody comes up and shouts, “Hey guy (がい)! I’ll give you $10,000 for that tree there, guy!” This guy must be crazy. That’s much more than your approximation of the value of this thing. But you sell it to the guy anyway.