What on earth….?

It’s scenes like this that make living in another culture so interesting. What on earth is this man doing? At first as I approached I thought he was using a meat cleaver to cut up some sort of food—and I wondered why he would be doing that out on the curb, but then I found that he was wielding a big rock to mash or cut up whatever the brown stuff is. And what is that brown stuff? Some sort of food? A root to be used for medicine? Some kind of nut with a hull to be knocked off? Petrified dog poop? I have no idea what is going on here although it may have been perfectly obvious to a local.